World number one Serena Williams extended her unbeaten run during 2003 to 17 wins and collected her third title of the year when she overcame the former world number one Jennifer Capriati in the final of the Nasdaq-100 Open in Miami.

However Williams had a scare on Saturday before she completed a 4-6 6-4 6-1 win, which took two hours and four minutes to complete in arduous 90-degree temperatures.

"I wasn't on my game today but I am going to do something about that," said Williams.

"I've been hanging out and relaxing for the past two weeks. I've slacked off but I will be back.

"Mentally I was up but I don't think physically I was up, and playing-wise there were things I wasn't doing."

Capriati played her best tennis of the year after going 2-0 down in the first set, sometimes matching the hardest hitter in the world from the baseline, often playing the more consistent tennis, and frequently getting partisan support from the crowd.

She broke back with some steady returning and some penetrating flat drives, broke again when Williams played an indifferent game, and for more than an hour had the champion looking disconcerted and edgy.

"I can definitely hang in there with her," said Capriati, who was not far from giving herself a memorable 27th birthday present.

"Her serve doesn't bother me too much."

Williams biggest problem was an unusually high unforced error ratio, though she was always intimidating when she found her range with her ground strokes, and unanswerably effective when she added patience to her weight of shot.

Her worst moments came after she had established a 4-0 second set lead when, remarkably Capriati broke back twice to get to 5-4 down.

Williams failed to serve out for the set at 5-3, double-faulting at set point and losing the game when she counter-hit a forehand into the net.

It required the champion's steeliest resolve and her most patient rallying to chisel back the advantage in the next game, breaking Capriati to 30 and establishing a sweaty parity.

It turned the match. Williams broke for 2-0 and 5-1 in the final set, quietening the crowd and easing her tension, and imposing her greater strength and physical fitness as Capriati tired.

"I saw she was starting to get a little tired in the third," said Williams.

"It was very hot out there. I told myself to get a quick start and to stay tough."

Asked whether the partisan crowd had bothered her much, Williams said: "It just motivated me more. Had she been playing anyone else I would have wanted her to win too."

Williams also appeared to rule out the possibility of lasting the year unbeaten - only to rule it back in again.

"It's impossible to win every match," she said. "If I could I would like to. I'm going to try - I don't know if it's possible."