The world number three appeared to be cruising when 5-2 up in the third set, before the scrappy Zuluaga forced Sharapova into numerous errors, forcing her to use five match points to win the nearly two hour contest.

"It was a big battle out there," said Sharapova, who will meet the winner of the Mary Pierce-Nadia Petrova match.

"I basically committed suicide when I had those four match points, especially when I came into the net and stayed in the middle.

"When you're not playing your best tennis, those are the matches where you finish, win or lose.

"But it's good to get through them, because I feel whenever I don't play that well, then the next day I come out and I do better and better."

Sharapova said she had briefly flashbacked to her semi-final loss to Serena Williams [Images] at the Australian Open, where she squandered three match points.

"It comes back in your mind," said Sharapova.

"Like you had four match points before and you're up 5-2, you were playing so good and all of a sudden either she picked up her game or you just started going downhill.

"But it's good to learn. I was frustrated when I got back to five-all, but then I pulled it together."

Two other Russians, Elena Dementieva and Svetlana Kuznetsova, set up a re-match of their 2004 US Open final when Dementieva beat Tatiana Golovin [Images] 2-6, 6-4, 6-4, while fifth seed Kuznetsova overcame Rika Fujiwara of Japan [Images] 6-3, 6-2.

"It's very good to have this kind of competition between us," Dementieva said. "I feel like I want to improve my game myself, because I want to be the best one."

Former champion Kim Clijsters [Images] continued her comeback from a wrist injury with a 6-2, 6-1 thrashing of Russia's [Images] Evgenia Linetskaya.

Clijsters said she had worked on improving her forehand in the time off and also decided to become more aggressive.

"I know in the past I was maybe a little bit too defensive in some situations," said Clijsters, who will face Conchita Martinez in the next round.

"But I'm feeling like I'm hitting the ball well when I'm under pressure."

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