British qualifier Elena Baltacha "fought her heart out" to record the biggest win of her career when she upset seventh seed Li Na of China at the Indian Wells WTA tournament on Friday.
Former world number one Justine Henin was also a shock loser, beaten 6-2, 1-6, 6-4 by Argentina's Gisela Dulko.
The 26-year-old Baltacha came from 5-1 down in the third set tiebreaker and saved two match points against the Australian Open semi-finalist before sealing a 7-6, 2-6, 7-6 victory in a contest that lasted two hours and 50 minutes.
It was her first success against a top-10 player, Li is ranked 10th in the world, and earned Baltacha a place in the third round against wildcard Alicia Molik of Australia.
"It's an unbelievable feeling," Baltacha, who won two qualifiers to reach the first round, told reporters.
"By the end of the match, I felt a little bit I was getting tired. At 5-1 (in the third set tiebreaker) I went into the zone and I felt really strong. I just fought my heart out."
Ranked 65th in the world, Baltacha broke into the top 100 for the first time last September and believes she has learned quickly by competing against the game's best.
"As I've played the big players this year, I've managed to gain quite a lot out of every single match and just build my game from that," she said.
In another upset, Dulko, who had lost to Henin here in straight sets in 2006 in their only previous meeting, broke the 2004 champion three times in an error-strewn final set before wrapping up the win in just under two hours.
Serving at 40-0, the 31st-seeded Argentine chased down a delicate drop shot by the Belgian before hitting a sharply angled crosscourt forehand winner to end the match.
The 25-year-old from Buenos Aires, who will play fifth seed Agnieszka Radwanska of Poland in the next round, then sank to her knees in disbelief as the fans watching on the stadium court applauded.
"It feels great," Dulko said in a courtside interview. "I am so excited, so happy. She (Henin) is an unbelievable champion and to beat her on this court is very special.
"I was really emotional out there. I couldn't believe at the beginning I actually won the match."
Henin, a dangerous wildcard entry, had been competing in her first tournament since losing to American Serena Williams in the Australian Open final in late January.
"It was a tough day today and I've never really been into the good rhythm," the Belgian said. "It proves that I have a lot of things to work on, and that's what I'm going to do in the next few days and few weeks."
Henin, a seven-times Grand Slam champion, had reached successive finals since returning to the circuit this year after quitting the game in 2008.
In other second-round matches, fourth-seeded Russian Elena Dementieva beat Olga Govortsova of Belarus 6-4, 4-6, 6-0 and 10th-seeded Maria Sharapova also had to work hard before winning 4-6, 7-5 6-2 against fellow Russian Vera Dushevina.
Second seed Caroline Wozniacki of Denmark battled past American Vania King 5-7, 6-2, 6-4 after clawing her way back from 4-1 down in the third set.