Images from matches played on Day 4 of the Australian Open at Melbourne Park on Thursday
Defending champion Roger Federer needed to knuckle down to end the feisty challenge of hard-hitting German Jan-Lennard Struff with a 6-4, 6-4, 7-6(4) win in the second round of the Australian Open on Thursday.
Federer coasted through the opening sets under the lights at Rod Laver Arena but was dragged into a scrap in the third as the 55th-ranked Struff broke his serve and took the match into a tiebreak on a steamy night.
Struff saved a match point with a searing backhand down the line but fell on the second when Federer crunched a huge serve into the corner.
Federer will meet French 29th seed Richard Gasquet for a place in the last 16 as he continues his bid for a 20th Grand Slam title.
Djokovic survives Melbourne furnace to beat Monfils
Six-time Australian Open champion Novak Djokovic fought back from a set down to beat a gallant Gael Monfils 4-6, 6-3, 6-1, 6-3 in unforgiving heat on Thursday.
Djokovic, untroubled by scorching conditions at Melbourne Park, beat the Frenchman -- taking his head-to-head count to 15-0 -- to move into the third round.
The 14th seeded Serb will play Spain's Albert Ramos-Vinolas next.
Struggling Wawrinka knocked out by Sandgren
Hobbling former champion Stan Wawrinka was knocked out of the Australian Open by American Tennys Sandgren on Thursday, losing 6-2, 6-1, 6-3 on the Margaret Court Arena.
Sandgren, 26, played rock-solid tennis to claim only his second grand slam singles victory having opened his account against Frenchman Jeremy Chardy in the first round.
Zverev tested but moves to third round
Alexander Zverev endured a mid-match lapse but steadied to defeat Peter Gojowcyzk 6-1, 6-3, 4-6, 6-3 in an all-Germany battle and reach the third round of the Australian Open on Thursday.
With the thermometer peaking at a stifling 40 degrees Celsius (104 F), the 20-year-old fourth seed was grateful for the relative cool of the evening and looked set for an early night as he raced through the opening two sets under the lights at Hisense Arena.
That was until 62nd-ranked Gojowczyk rallied to break Zverev in the third game of the third set and held the advantage bravely to make a game of the contest.
Chastened, Zverev knuckled down to deny his opponent a look at his serve in the final stanza and sealed the match with an ace to set up a next generation clash with South Korean talent Chung Hyeon.
Maria Sharapova suffered a late wobble in the blazing centre court heat before easing past 14th seed Anastasija Sevastova 6-1, 7-6(4) to reach the third round of the Australian Open on Thursday.
With the temperatures soaring, the former champion fired a barrage of winners past the Latvian to roar through the first set in 23 minutes at Rod Laver Arena.
Sharapova wavered when serving for the match at 5-4, allowing Sevastova to drag the match into a tiebreak, but the Russian doubled down on her baseline firepower to raise three match points quickly.
She closed out the match on the second when Sevastova clubbed a forehand long and will next meet the winner of 2016 champion Angelique Kerber for a place in the last 16.
Halep dashes past Bouchard into third round
Top seed Simona Halep eased fears over her fitness with a brisk 6-2 6-2 victory over Canada's Eugenie Bouchard to reach the third round of the Australian Open on Thursday.
The Romanian World No 1 sprained her ankle in her first round match at MelbournePark on Tuesday but showed no sign of restricted movement in a 65-minute romp on Margaret Court Arena.
Marching around the court like she meant nothing but business, Halep broke Bouchard seven of the eight times the Canadian served to set up a third round meeting with American Lauren Davies.
Bouchard, who beat Halep in the 2014 Wimbledon semi-finals, had her moments but made 26 unforced errors, conceding defeat with the last of them after Halep had fired down a huge forehand which she could only balloon wide of the court.
Former world number one Angelique Kerber celebrated her 30th birthday on Thursday with an emphatic 6-4, 6-1 win over Donna Vekic at the Australian Open to set up an intriguing third round clash of former champions with Maria Sharapova.
The resurgent German, who broke a 27-tournament title drought with victory at the Sydney International in the leadup, is now riding a seven-match winning streak as she looks to recapture the form that propelled her to the 2016 title at MelbournePark.
Kerber was uncomfortable in her skin as the top seed during last year's tournament, when she lost in the fourth round to American CoCo Vandeweghe, but ranked 21st this year, she looms as a dangerous floater in the draw.
In scorching conditions at Margaret Court Arena, she gave 52nd-ranked Vekic the run-around with a series of deft drop-shots and closed out the one-sided match with a confident cross-court smash.
Born in the same year of the Australian Open's debut at MelbournePark, Kerber soaked up a birthday serenade from the terraces during her post-match interview on the court.
"It's just amazing how the time is flying," said Kerber, who struggled for form through a difficult 2017 season.
"I'm feeling good, it's good to win today, of course, on my birthday.
"Now I think the work pays off and it's just the beginning of the year."
Injured Del Potro battles through to third round
Former US Open champion Juan Martin Del Potro battled an apparent thigh injury and sapping heat to down Russia's Karen Khachanov 6-4, 7-6(4), 6-7(0), 6-4 and reach the third round of the Australian Open on Thursday.
The 12th seeded Argentine had a medical timeout in the fourth set and continued to have treatment on his thigh during a change of ends but stayed on his legs to close out the taxing three hour 45-minute tussle at a sweltering Hisense Arena.
Del Potro, famous for toppling Roger Federer in the 2009 final at Flushing Meadows, was thrilled to advance, having missed the last three tournaments in Melbourne due to a string of injuries.
"I didn't expect to play this kind of match, I prefer to watch on TV," joked the 29-year-old, a twice quarter-finalist in Melbourne, during his post-match interview on court.
"I'm so happy to be playing in Melbourne after many years.
"I had pain everywhere but I'm still standing up."
Although disappearing in the third set tiebreak as Khachanov won 14 successive points in a fury of hard hitting, Del Potro captured the decisive break in the fifth game of the fourth set and held on grimly as his leg troubled him.
Clutching at the back of his thigh between points, last year's US Open semi-finalist remained solid on serve, however, and fought hard to push the powerful Russian to the wall.
On match point, he wound up his huge forehand and moved in for the kill but missed the straightforward shot down the line, raising a gasp from the crowd.
He steadied to win another match point and moved into a heavyweight third round clash with Czech former semi-finalist Tomas Berdych when the Russian netted a forehand.
Del Potro was impressed with the weapons of 21-year-old Khachanov, one of a string of rising Russians boasting prodigious firepower.
"Guys are so strong, I feel I am getting older for sure," he said.
"They play so hard. He hit harder than me.
"I had to run a lot but I think I took my chances to win the match and I'm so happy to go through."
Goffin's hopes over as he succumbs to Benneteau
Dark horse David Goffin's Australian Open hopes went up in smoke as he fell to a 1-6, 7-6(5), 6-1, 7-6(4) to French veteran Julien Benneteau in round two on Thursday.
The Belgian seventh seed dominated the opening set in ferocious conditions but the match changed direction after 36-year-old Benneteau won the second set on a tiebreak.
Goffin was listless in the third set as Benneteau moved ahead and fell a break down in the fourth, saving a match point on his own serve at 3-5.
World number 59 Benneteau had an attack of the nerves as he tried to close out the match, throwing in a couple of double-faults to allow Goffin to level at 5-5.
But he got the job done in the tiebreak to reach the third round of a grand slam for the first time since 2013.
Muguruza outfoxed by Hsieh in second-round defeat
Third seed Garbine Muguruza became the latest big-name casualty at the Australian Open as she lost 7-6(1), 6-4 in the second round to tricky Taiwanese doubles specialist Hsieh Su-wei on Thursday.
In searing heat on Rod Laver Arena, the powerful Wimbledon champion never got to grips with 88th-ranked Hsieh's unusual game style and looked totally perplexed by the end.
Muguruza had battled back from 5-2 down in the opening set but 32-year-old Hsieh, who plays double-handed on both sides, pulled out all the stops to take the tiebreak 7-1.
Hsieh pulled clear in the second set with her relentless accuracy but faltered with the winning line in sight, dropping serve at 5-2.
Muguruza double-faulted at deuce in the next game to give Hsieh a match point but survived and held serve to ask the question of Hsieh's nerve for a second time.
There would be no escape this time as Hsieh guided away a backhand winner on her second match point to claim the biggest singles victory of her 17-year career.
Muguruza joins other seeds Venus Williams, Sloane Stephens, Coco Vandeweghe, Kristina Mladenovic and Johanna Konta as early departures from the women's draw.
Hsieh will face Poland's 26th seed Agnieszka Radwanska for a place in the fourth round of a grand slam singles for only the second time, having reached that stage 10 years ago here.
Thiem sees off Kudla challenge in marathon match
In other results, fifth seed Dominic Thiem rallied from two sets down for only the second time in his career to beat American qualifier Denis Kudla 6-7(6), 3-6, 6-3, 6-2, 6-3 in the second round.
Two-time semi-finalist Tomas Berdych recorded 42 winners, including 12 aces, to overcome Spaniard Guillermo Garcia-Lopez 6-3, 2-6, 6-2, 6-3 in the second round.
Eighth seed Caroline Garcia booked a place in the third round after beating Czech Marketa Vondrousova 6-7(3), 6-2, 8-6 after almost two and a half hours of play on Hisense Arena.
Two-time Australian Open semi-finalist Agnieszka Radwanska rallied from a set and a break down to beat Ukraine's Lesia Tsurenko 2-6, 7-5, 6-3 to reach the third round.
Sixth seed Czech Karolina Pliskova needed just 44 minutes to see off Beatriz Haddad Maia of Brazil 6-1, 6-1, while American Madison Keys, a US Open finalist last year, took just 41 minutes to beat Russian Ekaterina Alexandrova 6-0, 6-1 in the second round.
Powerful Pera sends ninth seed Konta out
World No 123 Bernarda Pera sent ninth seed Johanna Konta tumbling out of the second round of the Australian Open on Thursday with a 6-4, 7-5 upset in blazing sunshine on court two.
A lacklustre serving display from the British number one allowed lefthander Pera ample opportunity to showcase her powerful returns off both sides and the 23-year-old American duly delivered.
A single break of serve for 5-4 was enough to sew up the first set after 39 minutes when Konta sent a backhand long and lucky loser Pera was soon over the Briton's serve in the second.
Konta, a semi-finalist at MelbournePark in 2016 and quarter-finalist last year, saved four match points but Pera was not to be denied and set up a meeting with Barbora Strycova when the Briton fluffed an overhead volley.
Late in the day, Ashleigh Barty, backed by a roaring home support on Rod Laver Arena, rallied from a set down to beat Italian Camila Giorgi 5-7, 6-4, 6-1 in the second round.
She will next face Japan's Naomi Osaka, who defeated 16th seed Elena Vesnina 7-6(4), 6-2.