Nick Kyrgios turned on the style in time to beat Ukraine's Alexandr Dolgopolov and set up a semi-final against top seed and holder Grigor Dimitrov at the Brisbane International on Friday.
The mercurial Australian huffed and puffed in a miserable first set but eventually found some rhythm to come through a tricky encounter 1-6 6-3 6-4.
Bulgarian Dimitrov also had to battle hard against Britain's Kyle Edmund, winning 6-3 6-7(3) 6-4 in two hours and 23 minutes at the Pat Rafter Arena.
Kyrgios, who will be under the home spotlight at this month's Australian Open, made 36 unforced errors against Dolgopolov but there were 27 winners too.
"As bad as it is to say, it's kind of like a tap. I can turn it on when I want to," the third seed told reporters.
"I'm feeling pretty good. I'm hitting the ball well and I'm serving really well. So the first two matches of the year, I've got through two tough three-setters," added Kyrgios, who beat compatriot Matthew Ebdon 6-7(3) 7-6(5) 6-2 in the second round.
"The only positive I can say about losing that first set (against Dolgopolov) is I'm putting myself in some pressure situations and getting some more court time out there which is good... I've got to try and maintain as much energy as I can."
Dimitrov was in control against Edmund as he took the first set but was dragged into a second-set tiebreak which the Briton edged to set up the decider.
Dimitrov, who survived two match points to beat local hope John Millman in the previous round, needed a solitary break to close out the match.
Kyrgios was joined in the last four by fellow Australian Alex De Minaur as the teenager followed up his win over Milos Raonic by beating American qualifier Michael Mmoh 6-4 6-0.
De Minaur will play unseeded American Ryan Harrison for a place in the final. Harrison was leading 7-6(6) 4-2 when Uzbekistan's Denis Istomin retired from the contest.
Siniakova tames Sharapova, faces Halep in final
Czech defending champion Katerina Siniakova fended off Maria Sharapova in a fiercely contested match at the Shenzhen Open on Friday to set up a final with world number one Simona Halep.
Siniakova fired 27 winners and 10 aces to prevail 6-2, 3-6, 6-3 but was made to work hard for the win after Russian Sharapova rediscovered her rhythm midway through the contest.
After losing the first set, Sharapova attacked Siniakova's serve to seal an early break in the second set.
The five-time Grand Slam champion gave little away after that and levelled the contest at one set apiece.
A stinging backhand down the line gave Siniakova a decisive break in the final set and the sixth seed hung on to close out the match in just under two hours.
Halep beat fellow Romanian Irina-Camelia Begu 6-1, 6-4 in one hour 29 minutes to claim a second career final spot at Shenzhen.
The top seed broke Begu early in the contest to race into a 4-1 lead. Begu sent a forehand wide in a see-sawing sixth game as Halep broke again and took the first set on serve.
Fourth seed Begu, seeking a first win over Halep at her sixth attempt, fought back to lead 3-2 in the second set but Halep eventually subdued the comeback attempt to seal victory.
"It was a tough match," Halep said in a courtside interview. "I know she is a strong player and in the second set you could see she was improving her game so it was a tougher battle.
"I think I was strong enough to stay there and hit the ball stronger in the end because the energy (from Begu) was falling a little bit. I came back, I served pretty well in the last game and I'm pretty proud of my victory today, it was a tough one."
Thiem, Rublev book semi-final spots in Doha
Top seed Dominic Thiem and Russian Andrey Rublev progressed to the Qatar Open semi-finals in Doha after grinding out victories over Stefanos Tsitsipas and Borna Coric on Thursday.
Greece's Tsitsipas, who ousted French fifth seed Richard Gasquet on Wednesday, took the early lead in the first set but Thiem, the only seeded player still in contention for the season-opening title, fought back to win 7-5, 6-4.
"I was serving well again today and returning well. That's what I was working on in the off-season so it already pays off now," Thiem said.
Croatian Coric was expected to overcome Rublev after beating Pablo Carreno Busta in the opening round but the 20-year-old Russian won 6-3, 7-5 to set up a semi-final against Guido Pella.
Both Pella and his quarter-final opponent Mirza Basic were surprise contenders in the last eight after knocking out top seeded players and the Argentine world number 64 cruised to a 6-2, 6-3 victory over the Bosnian.
World number five Thiem will face Gael Monfils in the last four after the Frenchman beat German Peter Gojowczyk 6-3, 7-6(6).
Nishikori set to launch comeback in Newport Beach
Japan's Kei Nishikori plans to launch his comeback at the inaugural Challenger Tour event in Newport Beach, California, beginning Jan. 22, the organisers said.
The 28-year-old was forced to withdraw from the Australian Open on Wednesday as he continues to recover from a wrist injury.
Nishikori has been on the sidelines since August when he fell to Gael Monfils at the Rogers Cup in Montreal. He finished 2017 with a 30-13 win-loss record.
"I am very excited and looking forward to getting back on the court in January," Nishikori said in a statement.
"The Oracle Challenger Series is a perfect event in a great Southern California location to help me get some match play. This will be a great opportunity to face some high-level competition."
Nishikori, currently ranked 22 in the world, also plans to compete at the Challenger event in Dallas, Texas, which begins on Jan. 29.