Caroline Wozniacki's first match since losing the world No.1 ranking ended dramatically on Wednesday at the Dubai Championships when opponent Anna Chakvetadze collapsed on court while serving for the second set.
Wozniacki, who was toppled by Kim Clijsters in the WTA rankings on Monday, won the first set 6-1 of the second round match but was struggling at 5-3 down in the second when her Russian opponent fell to the ground.
Top seed Wozniacki joined medical staff in assisting Chakvetadze who, after several minutes of attention decided to continue but played just one more point before retiring.
It was later announced that she was suffering from a gasto-intestinal illness.
"It was a shock. It was scary," said Dane Wozniacki, who can reclaim the world number one spot by reaching the semi-finals.
"I mean, she's a good friend of mine. Doesn't matter, but to see someone collapse on the other side, it's not a nice sight," she added.
Chinese fifth seed Li Na, runner-up to Clijsters at the Australian Open, wasted four match points on the way to a 6-7, 7-6, 6-2 defeat by Yanina Wickmayer.
Leading 6-2 in the second set tiebreak she looked set for a routine victory but her Belgian opponent fought back to take it 10-8. Wickmayer then dominated the closing stages of the deciding set, winning the final four games.
Seventh seed Victoria Azarenka was fortunate to survive a strong challenge from Chinese qualifier Shuai Peng, needing two hours 23 minutes to earn a 4-6, 6-2, 7-6 victory.
"It's the first match and a tricky opponent," Belarus's Azarenka told reporters.
"I didn't really play my best tennis but I'm glad that I fought hard today, and in the important moments I stayed there," she added.
Svetlana Kuznetsova and French Open champion Francesca Schiavone will have a re-match of their epic three hours 44 minute battle at the Australian Open after they both came though their second round matches.
Kuznetsova needed two and a half hours to overcome Bulgaria's Tsvetana Pironkova 5-7, 6-2, 6-4 while Italy's Schiavone beat Shuai Zhang of China 6-3, 6-1.
Apart from Li the top seeds advanced with ease as Russian second seed Vera Zvonareva, Australian fourth seed Samantha Stosur, sixth seed Jelena Jankovic, eighth seed Agnieszka Radwanska and ninth seed Shahar Peer of Israel all posted straight sets victories.
