Maria Sharapova had to battle back from a set down to beat Venus Williams at the Sony Ericsson Open in Miami.
Sharapova could now play Serena Williams in the next round
It was an error-strewn affair, but Sharapova held her nerve at the last to win 2-6 6-2 7-5.
Agnieszka Radwanska caused the first major upset with a 4-6 6-3 6-2 win over fifth seed Martina Hingis.
And Justin Henin narrowly avoided the same fate, coming from 5-1 down in the third set to beat Virginie Razzano 6-2 2-6 7-6 (7-5).
Sharapova conceded that the windy conditions were a factor in the scrappy nature of her win over Williams.
I need to recharge my whole body, and mostly my head
Williams made 50 unforced errors and served up 12 double faults, one less than Sharapova, who also committed 35 unforced errors.
"You know you're not going to play your best tennis," Sharapova said. "You're always going to have to adjust.
"You definitely can't get frustrated. But I'm a fighter and a big competitor.
"That's why I play the sport. I enjoy the battle of it, and a lot of my matches, it depends on who fights more in the end."
Sharapova could now face the other Williams sister, Serena, in the fourth round.
But the night match between the Australian Open champion and Czech Lucie Safarova was postponed until Monday when the rain that has plagued the tournament struck again.
Radwanska, a former Wimbledon and French Open junior champion, was surprised with her two-hour victory over Hingis.
I love to play under pressure
"Before the match, I didn't believe I could beat her," said the 18-year-old world number 49. "And a few years ago she was my favourite player."
Hingis, on the other hand, believes she needs to focus if she is to stop her run of bad form.
"I just wasn't able to pull it off today," the Swiss former world number one said. "It's been like that the last three, four weeks.
"I'm getting tired of losing matches which I'm supposed to win. I need to recharge my whole body, and mostly my head."
Henin, on the other hand, showed her trademark determination after finding herself two points from defeat against Frenchwoman Razzano.
"I came back from nowhere," Henin said. "It's in those spots when I play my best tennis. I proved it many times in the past. I love to play under pressure."
There were no problems for third seed and defending champion Svetlana Kuznetsova, who overcame Croat Jelena Kostanic Tosic 6-4 6-2, and fourth seed Kim Clijsters, who beat Samantha Stosur 6-4 6-2.
Sixth seed Nadia Petrova also progressed as she thrashed fellow Russian Ekaterina Bychkova 6-1 6-1.
But seventh seed Jelena Jankovic was ousted by Italian Mara Santangelo 2-6 7-6 6-4.