The high-quality match was competitive from start to finish, with just one break deciding the first set and three match points needed in the second.

Fourth seed Azarenka, who was seeking her fourth career title, rallied well with Williams but could not match her serving power or the strength of her ground strokes.

The opening set was effectively decided on a double-fault at 3-2 after Williams had forced a backhand error to set up break point.

Azarenka's second serve was called in but Williams appealed and the Hawkeye line-calling system showed a fault.

Williams had difficulty serving out the set at 5-3, hitting two double-faults and then facing a break point, which she saved with a forehand pass.

The American then broke to lead 1-0 in the second set when Azarenka netted a backhand.

A forehand error allowed the Belarussian to level at 3-3 and the set seemed destined for a tiebreak until another forehand pass gave Williams a decisive break for 6-5.

The final point was one of the best of the match, as each ran the other around in a rally before Azarenka strained to hit a forehand that failed to clear the net.

Meanwhile in Memphis, Tennessee, Sam Querrey broke top seeded Andy Roddick's serve twice in the deciding set to stun the defending champion 7-5, 3-6, 6-1 in the quarterfinals of the Memphis Championships on Friday.

Women's top seed Maria Sharapova advanced to the final defeating fifth ranked Petra Kvitova of the Czech Republic 6-4, 6-3.

American world number 31 Querrey took charge of the deciding set after he battled to deuce in the second game before Roddick double faulted to gift his compatriot a 2-0 lead.

"Today I played one sloppy game in the third set and that was it," Roddick said. "Sometimes at this level there's not much in between it." Querrey said he knew he had to take advantage of Roddick's errors.

"You're not going to get that too many times from Andy, but I'll take it," he told reporters.

"When that rare opportunity comes you've just got to take advantage of it. I thought I did a good job there, and just kept the momentum going and played an unbelievable third set." Querrey consolidated his advantage with another break two games later and eased to victory for the loss of just one more game.

In the opening set, the big serving pair went toe-to-toe until the 11th game when Querrey broke Roddick to forge a 6-5 lead and took the opener in style with his 10th ace.

Roddick built on an early break in the second set to even the contest before Querrey, who sent down 16 aces overall, regrouped in the third to gain revenge for a semifinal defeat to the world number seven in San Jose a week ago.

"It was disappointing," said Roddick. "I felt like it was the opposite of Sam's and my match of last week. I felt like I had the better end of the first two sets and (yet) we were even."

The first set between Sharapova and Kvitova featured five breaks of service, three by Sharapova. And that trend continued into the second as each player broke serve in the first two games.

Sharapova would once again break Kvitova's serve in the seventh game to take a 5-3 lead, which she would not relinquish.

The Russian will meet unranked qualifier Sofia Arvidsson of Sweden in the final on Saturday. Sharapova has won the only previous match between the two, though Arvidsson won the tournament in 2006.