Serena, Azarenka play it again at US Open final

Top seed Williams, chasing a 17th Grand Slam title, crushed China's Li Na 6-0, 6-3 while Azarenka took an error-strewn 6-4, 6-2 win over Italian veteran Flavia Pennetta.

Williams, 31, seeking a fifth title in New York, will be the overwhelming favorite in Sunday's final as she boasts a 12-3 career lead over her 24-year-old opponent.

However, not all is lost for Azarenka, who beat the American in the Cincinnati final just before the US Open.

"I just try hard and when I hear young and old voices in the crowd shouting 'Go Serena, Go Serena' it makes me feel so special," said Williams.

"When I play Victoria we always have good matches. She's a great player who lifts her game when it counts."

Williams raced through the first set in just 29 minutes with three breaks of serve as Chinese fifth seed Li, playing in her first US Open semi-final, wilted under the American's trademark barrage.

It was Williams' fifth love-set of the tournament, having reached the semi-finals for the loss of just 13 games.

Li, the 2011 French Open champion, showed great resolve to make a fight of it in the second set, hitting back for 2-1 against a player who went into the match with an 8-1 career stranglehold over her.

Li saved six match points in the 13-minute eighth game of the second set but was finally beaten when a service return was dumped in the net, having hit just eight winners in the 87-minute tie.

"I was feeling I need more practice. It's not about the technique. I should not be nervous because it's not first time I play semis," said Li.

World number two Azarenka reached her second successive US Open final with a win over Italian veteran Pennetta, the world number 83, in a match featuring 13 breaks of serve.

It was Australian Open champion Azarenka's third successive semi-final appearance in New York, but she will need to step it up in the final after committing six double faults and 25 unforced errors.

"I am so excited to be back in the final and get the chance to fight for the trophy," said Azarenka.

"It was a great match today. There were lots of emotions. It was tricky because I struggled to find any rhythm and Flavia is such a great fighter. I couldn't get a ball in play."

She added: "In the final, I will be facing a great player. I will have to give it all I have got, all my heart, all my body and all my mind."

In a tense, error-hit first set there were seven breaks of serve in 10 games with Azarenka, who had spent two hours more on court getting to the semi-finals than her opponent, struggling to impose her authority.

Azarenka eventually closed out the opener on a sixth point after a 10-minute game.

Pennetta, bidding to be the first Italian woman to make the US Open final after missing the 2012 tournament due to a wrist injury, had saved two of them with a couple of scintillating groundstrokes, one off each wing.

It wasn't pretty for Azarenka, who served up five doubles faults in the set and hit 18 unforced errors.

The second set also got off to a rocky start with three successive breaks before Azarenka managed to hold for 3-1 and break the flagging Italian again for a 4-1 advantage.

Pennetta called for water at the changeover but would have been better off pleading for mercy after being broken for the seventh time in eight service games.

The Italian, a former top 10 player who had defeated three seeded players to reach the last four, clung on and broke back before she surrendered the advantage yet again, dropping serve for the eighth time.

It was her last chance. Azarenka went to three match points in the eighth game and claimed victory after 94 minutes with a wrong-footing forehand.

"I didn't serve really well, but neither did she. There was a lot of wind in the court and it's not easy to serve," said Pennetta.