Canada's Aleksandra Wozniak, meanwhile missed on a match point as she lost a third-round, three-hour struggle to Venus Williams on Sunday 4-6, 6-4, 7-6 (5) in the women's draw at the Sony Ericsson Open in Key Biscayne, Fla.

The native of Blainville, Que., had a chance to score the upset in a hard-fought marathon on the showcase at Crandon Park but sent a forehand long in the tenth game of the final set.

"You have to close out these tough matches," said Wozniak. "I had that match point against her but I wasn't able to stay mentally tough. You need to keep fighting.

"We both played well. It was a matter of converting on the important points."

Williams, who won a trio of Miami titles starting 14 years ago and whose ranking has dropped to 134 as she plays for the first time since the US Open, managed to hang on in a match featuring 32 break points and 14 conversions.

The 31-year-old American finally earned victory in the tiebrekaer as Wozniak committed a final error on a second Williams match point after saving the first.

"It's never easy in the intense moments, a lot goes on in the mind," said Wozniak. "You are fighting and you want every point so badly, you want to make an ace or hit a winner. This was a tough one to lose."

Wozniak, ranked 65th in the world, had never faced the elder Williams sister but had defeated her sister Serena in a 2008 Stanford semifinal on the way to that title. Wozniak came to Miami with confidence after winning a lower-level event last week in Nassau, Bahamas.

Wozniak opened with authority as she broke Williams in the first game but was then forced to save six break points on her first two service games to maintain the margin.

Wozniak struck 30 winners and 39 unforced errors to 70 unforced from Williams.

"Overall it was positive, so I can't be too disappointed, even if I am right now," said Wozniak. "I came close against a top player, but I have to win these matches."

Williams has been suffering with an immune system disease which saps her energy and was playing in he first event since the US Open.

Earlier, Canadian Milos Raonic withdrew from the men's draw with an ankle injury.

The 21-year-old from Thornhill, Ont., was unable to take the court Sunday against British fourth seed Andy Murray for their third-round match after rolling an ankle during training.

Raonic, however, expects to be ready for his next event in Monte Carlo in April.

"I was just moving back and I rolled over my ankle and ended up spraining it," said Raonic, who consulted his doctor in Spain over the problem and will now spend a few days at home in Canada.

Raonic and doubles partner Kevin Anderson quit their Saturday doubles match after three games when the Canadian could not go on against third seeds Michael Llodra and Nenad Zimonjic, former partner of Toronto's Daniel Nestor.

"I don't know too much about it right now, but in the doubles it wasn't getting better," said Raonic. "This morning it was a bit painful on pretty much every movement. Against the calibre of player I'd be up against, to play at 40 per cent didn't really didn't make much sense.

"The doctor in Spain doesn't think it's anything big. It probably just needs a couple days of rest, but active rest. With treatment and so on, it should be okay within a week or so."

It was Raonic's second injury blow in as many seasons. The 26th seed in Miami was forced to withdraw last summer from Wimbledon in the second round after injuring his hip in a match against Gilles Muller.

Except for one Davis Cup match, Raonic was out of action until October.

"It's frustrating, but you must look at the big picture," said the Canadian with two ATP titles this season. "Everything is going well, obviously it would be more frustrating if things were going poorly.

"Even though if I might have some worries about something, I'm pretty good at coming back pretty quickly."

In other men's action:

  • Rafael Nadal (2), Spain def. Radek Stepanek (25), Czech Republic 6-2, 6-2.
  • Janko Tipsarevic (9), Serbia, def. Alexandr Dolgopolov (18), Ukraine, 6-4, 5-7, 6-2.
  • Grigor Dimitrov, Bulgaria, def. Tomas Berdych (7), Czech Republic, 6-3, 2-6, 6-4.
  • Gilles Simon (13), France, def. Jurgen Melzer (22), Austria, 7-6 (5), 6-4.
  • Jo-Wilfried Tsonga (6), France, def. Philipp Kohlschreiber (32), Germany, 6-4, 7-6 (2).
  • Kei Nishikori (16), Japan, def. Lukas Rosol, Czech Republic, 6-4, 6-2.
  • Florian Mayer (19), Germany, def. John Isner (10), United States, 6-4, 6-2.

In the women's singles draw Sunday:

  • Victoria Azarenka (1), Belarus, def. Heather Watson, Britain, 6-0, 6-2.
  • Dominika Cibulkova (16), Slovakia, def. Zheng Jie, China, 6-2, 6-0.
  • Marion Bartoli (7), France, def. Simona Halep, Romania, 6-4, 7-6 (6).
  • Garbine Muguruza Blanco, Spain, def. Flavia Pennetta (24), Italy, 6-2, 1-6, 7-6 (6).
  • Maria Kirilenko (22), Russia, def. Ksenia Pervak, Kazakhstan, 6-2, 6-1.
  • Ana Ivanovic (15), Serbia, def. Daniela Hantuchova (20), Slovakia, 6-2, 7-6 (2).
  • Agnieszka Radwanska (5), Poland, def. Silvia Soler-Espinosa, Spain, 6-1, 6-2.
With files from The Associated Press