KEY BISCAYNE, Fla. -- Serves turned shaky and willpower wilted Thursday in the scorching South Florida sun, which turned the Nasdaq-100 Open into a test of subtropical stamina.

Old-timers Vince Spadea and Jonas Bjorkman passed, notching first-round victories. Teen prodigy Richard Gasquet failed, quitting in the third set with a heat-related headache.

And there was Meilen Tu, who won a midday marathon and then left the stadium court on a stretcher with heat exhaustion.

"I was hyperventilating, couldn't breathe and kind of collapsed,'' Tu said. "Everything shut down after I shook the umpire's hand.''

The temperature peaked at 88 degrees, just short of the record for the date.

"It was very hot,'' said Spadea, who beat Christophe Rochus 6-3, 6-4. "I was pacing myself and trying to give him all the energy I had.

"But it was a hot day. The wind didn't help much. And I'm from Florida, so what I say counts.''

For the second day in a row, the WTA Tour activated its rules for extremely hot weather, allowing a 10-minute break after the second set. Tu barely made it to the finish, beating Bethanie Mattek 6-1, 6-7 (4), 7-6 (4) in 2 hours, 53 minutes.

Tu began to feel the heat during the second set. She overcame cramping in both thighs, both calves and her right forearm.

"To win a match like this, I will always remember it,'' she said. "I didn't think I would win.''

The precocious Gasquet, who at 16 is already ranked 112th, had to retire with fellow Frenchman Jean-Rene Lisnard leading 3-6, 6-1, 2-1.

Karol Kucera retired with an upset stomach trailing Fernando Verdasco 6-2, 4-0. But Bjorkman showed impressive fitness while rallying past Andre Sa 3-6, 6-4, 6-4.

Two injuries had nothing to do with the weather. Vladimir Voltchkov retired because of a recurring elbow injury trailing Francisco Clavet 6-0, 3-0. Goran Ivanisevic, the 1996 runner-up, withdrew before his match after cutting his left foot while wading in the Atlantic Ocean on Miami Beach.

Promising 18-year-old Croat Mario Ancic lost a 3-hour, 5-minute marathon to Franco Squillari 6-7 (5), 7-6 (4), 6-4.

The 1992 champion, Michael Chang, who plans to retire later this year, began his 12th and final appearance at Key Biscayne by beating Nicolas Kiefer 6-2, 6-2.

Chang next plays five-time champion Andre Agassi, renewing a rivalry that began when Chang was 10 and Agassi 12.

"It's never an easy match for me," Chang said. "Hopefully it's not an easy match for him. But it's definitely a match to be excited about."

Mark Philippoussis eliminated Feliciano Lopez 7-6 (5), 6-4.

In a later match, Anna Kournikova's prolonged slump continued with a dispirited 6-1, 6-4 loss to 16-year-old countrywoman Dinara Safina in the first round.

Playing for the first time since the Australian Open, Kournikova lost for the third time in four matches this year. She has dropped 24 of her last 30 games.

Still looking for her first career title, the Russian has been bounced in the first or second round in 19 of her last 24 tournaments.

Spadea's win was his first since 1999 at Key Biscayne, where he beat three top-10 opponents in the 1990s. A prolonged slump dropped his ranking to 229th, but he's now back in the top 50 for the first time since May 2000.

"I've had to work really hard,'' he said. "It's times like this week that I'm going to take full advantage of what I've done the past two years.

"It wasn't easy playing smaller events and trying to gain my ranking spot slowly. Now that I've started to make some bigger headway, I feel like I need to take advantage of it.''

Spadea has won 13 matches in 2003, matching his total for all of last year. His second-round opponent will be fifth-seeded Carlos Moya.

Information from SportsTicker was used in this report.