MASON, Ohio -- Serena Williams did enough to get a hard-fought victory.
Williams earned a sloppy 2-6, 6-2, 6-4 win over Caroline Wozniacki on Saturday to reach the final of the Western & Southern Open.
The top-seeded Williams bounced back from losing her first set of the tournament and committing 41 unforced errors, 20 more than Wozniacki, to beat the 12th-seeded Dane for the eighth time in nine career matches.
In the first men's semifinal, sixth-seeded David Ferrer earned his first trip to the tournament final in 11 appearances with a 6-3, 6-2 win over unseeded Julien Benneteau.
Williams had to shake off a tight lower back before turning her game around, she said.
"It was definitely feeling super tight in the match," she said. "That's when I really relaxed, to be honest. By then I was able just to go for more shots and come to the net more and just kind of just not have anything to lose."
She also tried to shorten points with booming serves, leading to getting just 58 per cent of her serves in play.
"I just had to go for rockets because I wasn't feeling great," she said. "I thought, 'Listen, I'm going to go out and just try to hit aces and see what happens.' It started working for me. I was like, 'OK.' Hopefully my arm will be OK tomorrow. We'll see."
Williams and Wozniacki both struggled with their serves, leading to a combined 15 service breaks, including the first five games of the third set. Wozniacki was broken in eight of nine service games in one stretch and connected on just 54 per cent of her first serves.
"I didn't get many first serves in," Wozniacki said. "When I did, they weren't placed very well. It's frustrating, because you lose a set 6-4 in the third and you only hold serve once.
"I actually broke Serena three times in the set. I don't think that happens very often to her either, so, you know, you feel like you're there and my all game was there.
"I was fighting. I was running. I was trying to take the ball early. I was returning well. Then my serve comes around and I can't seem to hold serve. It's frustrating thing when you're out there on the court."
Williams has never won the championship in five previous appearances. She lost a third-set tiebreaker to Victoria Azarenka last year.
Williams will play the winner of Saturday night's match between fifth-seeded Maria Sharapova and ninth-seeded Ana Ivanovic for the championship on Sunday.
With the win, Williams also clinched the U.S. Open Series women's title. Williams has won it three of the past four years and will attempt to set another record for the largest payout in tennis history at the U.S. Open -- $4 million ($3 million for winning the U.S. Open and a $1 million bonus for winning the U.S. Open as the series champion).
The two-time defending U.S. Open champion won both the U.S. Open Series title and the U.S. Open last year. She is the only woman to win the US Open Series bonus challenge three times (2011, 2013, 2014). No other woman has won it more than once.