KEY BISCAYNE, Fla. -- Weary winner Venus Williams stood near the net swatting souvenir balls to cheering fans, but a marathon match had taken its toll, and one of her attempts didn't even reach the stands.
Williams had already expended all her energy, erasing a match point and outlasting Aleksandra Wozniak 4-6, 6-4, 7-6 (5) in Sunday's third round at the Sony Ericsson Open.
Her career comeback now includes a come-from-behind win. Williams is playing in her first tournament since withdrawing from the U.S. Open last August after being diagnosed with a fatigue-causing autoimmune disease.
The three-set victory was her second in less than 48 hours, and took nearly three hours.
"I just kept coming back," Williams said. "I tried not to let anything discourage me."
Wozniak served for the match at 5-4 in the final set, but dumped a forehand in the net when she had a match point. Talking later about the situation, Williams claimed to be unaware Wozniak had been so close to victory.
"She had match point?" Williams said. "Oh no. Thank God I'm oblivious to the score a lot of times."
The tiebreaker swung Williams' way when she smacked an overhead that clipped the net cord before landing softly for a winner and a 4-2 lead. On the final point, she somehow found the strength to whack a 119-mph service winner.
"That's the serve I wanted -- just a big one to hopefully force the issue," Williams said. "Thank God it went in. Wow."
Nadal, seeded No. 2, defeated 33-year-old Radek Stepanek 6-2, 6-2 and has lost only six games in two rounds.
"Good, solid start of the tournament," Nadal said. "Two good matches, comfortable wins."
The No. 10-seeded Isner, coming off a runner-up finish at Indian Wells a week ago, lost to No. 19 Florian Mayer, 6-4, 6-2. No. 4 Andy Murray, the 2009 champion, advanced in a walkover when Milos Raonic withdrew because of a sprained right ankle.
The top-ranked Azarenka improved to 25-0 this year by beating wild card Heather Watson 6-0, 6-2.
On a sweltering spring afternoon, Williams looked lethargic at the outset, struggled with an erratic forehand and kept falling behind. She played with straps on her right ankle and right calf, and often seemed a step late to the ball.
"Wake up, Venus!" a fan shouted in the second set. Younger sister Serena, who plays her fourth-round match Monday, watched solemnly from the club section of the stadium.
"I didn't feel that great, and I was kind of starting to panic," Venus said. "I needed to calm down and try to figure out a strategy that was going to work a little better than what I was doing at the moment."
She managed to pull even after two sets, then fell behind 4-2 in the third set and looked increasingly weary. During one changeover she hung her head for 15 seconds before slowly lifting it to take sips from two drink bottles.
Wozniak looked fresher, but the wild card from Canada couldn't serve out the match. Instead, the opportunity unnerved her. She hit consecutive double-faults and committed unforced errors on the game's final three points, which made it 5-all.
Play continued for another half hour before another match point, this one held by Williams. After her service winner clinched the victory, she managed to raise both fists and muster a smile.
A former No. 1 and seven-time Grand Slam singles champion, Williams is ranked No. 134 and needed a wild card to enter the tournament. She's trying to improve her ranking enough in the coming weeks to qualify for the London Olympics.
"Whenever things look bleak, I think about the Olympics," Williams said. "That keeps me motivated."