The 23-year-old Russian was serving for the second set at 5-3. After a long rally that Wozniacki won, Chakvetadze wobbled before fainting. She was given extensive medical treatment during a seven minute delay and returned for one more point before forfeiting the match and tearfully hugging Wozniacki.
Organizers said Chakvetadze, who lost the first set 6-1, had a stomach illness.
Wozniacki said it was a "shock" to see someone she considers a good friend collapse so suddenly. When she approached her, Chakvetadze said she had felt dizzy.
"Suddenly, I just see her collapse on the court. I didn't know what happened," the 20-year-old Dane said. "It was a shock. It was scary. To see someone collapse on other side, it's not a nice sight. I just want to make sure she was OK."
Wozniacki, who needs to reach the semifinals in Dubai to retake the No. 1 spot she lost on Monday to Kim Clijsters, looked like she was coasting to an easy victory after winning the first set in 22 minutes. But then Chakvetadze woke up in the second and seemed on the verge of leveling the match - which clearly rattled the normally calm Wozniacki.
At one point, the 20-year-old Dane tossed her racket in frustration.
"In the first set, I didn't get into the game that much," Wozniacki said. "She was making a lot of mistakes. Suddenly, she started to go for it. I just need some time. I started playing better at the end of the second set."
In early matches, Grand Slam winners Francesca Schiavone and Svetlana Kuznetsova both won to set up their first clash since their nearly five-hour-long epic at the Australian Open.
Schiavone accounted for Chinese qualifier Zhang Shuai 6-3, 6-1 while Kuznetsova, a two-time runner-up in Dubai, took the long road to beat Tsevetana Pironkova of Bulgaria 5-7, 6-2, 6-4 for a third straight time.
The wins put them on course to meet on Thursday, more than three weeks since their fourth-round encounter in Melbourne went for 4 hours, 44 minutes in the longest women's Grand Slam singles in the Open era. Schiavone won.
Looking forward to the match, Schiavone smiled and said, "After two hours, I'll take the racket and put it in the bag.
"I really want to play against her because we know each other, we play good tennis and we can enjoy it and improve."
Kuznetsova leads their matchups 8-5 since 2003, but Schiavone has won the last two.
Second-seeded Vera Zvonareva beat Roberta Vinci of Italy 6-3, 6-1. The Russian, still seeking her first title in more than a year, has exited in the Dubai quarterfinals in the last two years.
"It's never easy to play Roberta, she's a tricky player," Zvonareva said.
Fourth-seeded Sam Stosur thrashed Pattaya Open runner-up Sara Errani of Italy 6-0, 6-1 in 55 minutes, and seventh-seeded Victoria Azarenka of Belarus overcame seven double faults to beat Chinese qualifier Peng Shuai 4-6, 6-2, 7-6 (5).
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