Emma Raducanu, Simona Halep and Iga Swiatek all came out on the winning side of three set matches while former world number ones Karolina Pliskova and Garbine Muguruza were upset in second round action at Indian Wells on Friday.
Raducanu's 6-1 3-6 6-1 victory over France's Caroline Garcia is the Briton's first at the WTA 1000 event as she looks to get her season on track after falling in the second round at the Australian Open and retiring from Guadalajara with an injury.
The reigning US Open champion came out hot in the Southern California desert, playing nearly flawless tennis to take the first set before Garcia responded forcefully in the second.
After exchanging breaks to begin the decider, Raducanu won the final five games to seal the win on a sunny day on Stadium One.
"It's amazing to be back and it's amazing to get my first win in the desert here," the 19-year-old Raducanu said in an on-court interview before a supportive crowd.
"I hope to come back for many years."
Halep's 6-2 4-6 6-2 win over Ekaterina Alexandrova followed a similar trajectory as the two-time major champion breezed through the first set before running into resistance in the second and running away with it in the third.
"It's always tough to play the first match of the tournament and she is a very difficult opponent," said Halep, who now holds a 3-2 lead in their head-to-head matches.
"But I'm happy that I could win. It's important at this stage."
Swiatek needed time to find her serve in her match against Ukrainian Anhelina Kalinina but once she did, the third-seeded Pole eased into the third round with a 5-7 6-0 6-1 victory.
With their wins, Halep and Swiatek remain on track for a possible semi-final clash.
In the wildest match and biggest upset of the tournament so far, Muguruza held a 6-0 3-0 lead over Alison Riske before the American staged an sensational comeback to win 0-6 6-3 6-1.
With the win the 31-year-old Riske notched her 10th career win over a top-10 player and her third in five matches against the Spanish two-time major champion.
"After the first set, it literally could not get any worse," Riske said in her on-court interview.
"So if I could try to get two balls in the court we might get somewhere. I was just trying to hang in there. I've played Garbine many times before and it's always been a battle."
In the day's other big upset, Danka Kovinic stunned big-serving Pliskova 2-6 7-5 6-4 in a hard fought two-and-a-half hour match.
The match was world number eight Pliskova's first of the year after the Czech was sidelined with a broken arm.
Swiss Belinda Bencic and Ukrainian Elina Svitolina were also eliminated while American teenager Coco Gauff and veteran Angelique Kerber advanced.
