Venus Williams fought back to down third seed Petra Kvitova 4-6, 7-5, 6-4 and reach the BNP Paribas Open third round, on Saturday, while Naomi Osaka got her title defence off to a flying start with a straight sets win over Kristina Mladenovic.
World number one Osaka beat Mladenovic 6-3, 6-4, the win under the stadium court lights sweet revenge for the reigning U.S. and Australian Open champion after she lost to the same opponent in the Dubai Duty Free Tennis Championships first round last month.
Osaka said it was the first time she had felt the pressure of defending a title.
"I've never been a defending champion before so I was pretty nervous and I'm glad I got the win," the Japanese 21-year-old said.
American Williams, 38, turned back the clock in the final two sets at Indian Wells, dialling up the speed on her first serves and playing stout defence to seal a win that looked unlikely when she was down a double break in the second set.
The seven-times Grand Slam champion threw her arms in the air and let out a roar when Kvitova sent a ball long on match point -- the Czech's 56th unforced error of the day.
Williams tipped her hat to the two-times Wimbledon champion after the hard-fought contest.
"She has been playing so well and you never know what's going to come off her racket," a beaming Williams said in front of a fawning crowd as night fell on her native Southern California.
"I was just happy to have your energy to get pumped up. I just love the battle."
Earlier, another American, Madison Keys, blew a late lead to fall 3-6, 6-1, 7-5 to German Mona Barthel.
The 17th-seed had the match on her racket serving with a 5-4 lead in the third set but lost three straight games, including her final service game to love, allowing the unseeded Barthel to advance.
Next up for Barthel is a meeting with countrywoman Julia Gorges, who beat Estonian Kaia Kanepi 6-3, 2-6, 6-3 behind seven aces in an evening match.
Unheralded Russian Ekaterina Alexandrova upset former world number one Caroline Wozniacki 7-5, 2-6, 7-5 in a battle that lasted nearly two-and-a-half hours in the evening session.
Alexandrova put her hands over her face in disbelief when Wozniacki was unable to return her serve on match point.
The 24-year-old will face Belinda Bencic in the third round on Monday after the Swiss cruised to a 6-4, 6-1 win earlier in the day.
Former world number one Angelique Kerber was nearly perfect en route to a 6-0, 6-2 dismantling of Yulia Putintseva, winning 93 percent of her first service points under sunny skies.
The eighth seed will meet red-hot Russian Natalia Vikhlyantseva in the third round after the qualifier crushed Spaniard Carla Suarez Navarro 6-2, 6-0.
Czech Karolina Pliskova, Latvian Anastasija Sevastova and Americans Danielle Collins and Christina McHale were among the other players who prevailed in their second-round matches on Saturday.
Auger-Aliassime outguns Tsitsipas at Indian Wells
Canadian teenager Felix Auger-Aliassime won a battle of young guns by beating ninth seed Stefanos Tsitsipas 6-4, 6-2 on Saturday to advance to the third round of the BNP Paribas Open.
The 18-year-old, the youngest player in the world top 100, fired an unreturnable serve on match point to take down the 20-year-old Greek -- the youngest player in the top 10.
While the outcome was an upset on paper, Auger-Aliassime held a 3-0 advantage over Tsitsipas when they met as juniors.
"I didn't know what to expect today because he's a completely different player (now)," said Auger-Aliassime after their morning match.
"I believe in myself. I thought I had my chances. I served really well today, so that was obviously a big key."
Next up for last month's Rio Open finalist is Japan's Yoshihito Nishioka, who defeated Spain's Roberto Bautista Agut 7-6(3), 6-4 in a chillier evening session.
World number one Novak Djokovic picked up steam during his second-round match against American Bjorn Fratangelo under the lights on the stadium court as he goes in search of his 74th ATP title.
Djokovic sprinted over to the stands to shake hands with his idol, 14-times Grand Slam champion Pete Sampras, immediately after the 7-6(5), 6-2 win.
"I was a bit nervous, I don't get to see Pete that often," the 31-year-old Serb told reporters.
"It's a thrill to see someone that I looked up to when I was a kid."
A sharp Philipp Kohlschreiber broke Nick Kyrgios twice en route to a 6-4, 6-4 win that took just over an hour.
Kohlschreiber deployed a wide variety of shots to keep the 23-year-old Australian guessing and managed to save all five of Kyrgios' break-point opportunities.
American qualifier Marcos Giron battled back to down 23rd seed Alex de Minaur 1-6, 6-4, 6-2 for the biggest win of his career.
Playing in just his fourth ATP tournament, the Southern Californian settled down after a shaky first set to dispatch the 20-year-old Australian.
Giron, 25, will be a heavy underdog when he faces Canadian 13 seed Milson Raonic, who pounded down 18 aces to send American Sam Querrey packing from Indian Wells for the second consecutive year with a 7-6(1), 6-4 victory.
France's Gael Monfils outlasted Argentina's Leonardo Mayer 6-4, 3-6, 6-3 under blue skies on the stadium court.
With the win Monfils, who won last month's Rotterdam Open, improved his 2019 record to 13-3.
He will next face Spaniard Albert Ramos Vinolas, who upset 15th-seeded Italian Marco Cecchinato in their second-round meeting.
Seventh seed Dominic Thiem toppled Australian Jordan Thompson 6-4, 7-5 to close out the action on Saturday.
The Austrian baseline specialist will next face France's Gilles Simon, who he has defeated in eight of 10 career meetings.
Third seed Alexander Zverev had a stress-free opening match of the tournament, winning 6-3, 2-0 over Martin Klizan, who was forced to retire with a right ankle injury in the second set.