Rafael Nadal will try to extend his unbeaten 2013 record on hardcourt when he faces American John Isner on Sunday in the final of the Cincinnati Masters.

Nadal defeated Czech Tomas Berdych 7-5, 7-6 (7-4) on Saturday to win his 14th straight match in the series. He takes a 3-0 record against big American Isner into the final at the last major tune-up prior to the start of the US Open a week from Monday.

Argentine Juan Del Potro double-faulted on a match point to hand Isner a lifeline, and the American seized it to carve out a 6-7 (5-7), 7-6 (11-9), 6-3 win in their semi.

Isner looked down and out as he trailed a set, but with an opponent complaining of wrist pain during the pre-grand slam, he was able to find a way to win.

Nadal’s only weak point against Berdych might have been his uncharacteristic six double-faults in the second set, which he remedied with his usual bludgeoning groundstroke to take the victory in just over two hours.

The Spaniard who can return to second in the world if he wins his ninth title of the season, struck 38 winners.

He is seeking a second straight Masters 1000 hardcourt title after winning Montreal a week ago. Nadal came onto court less than 24 hours after beating Roger Federer in the quarters.

“I have adapted well here. I played a great match with Roger. I felt I played well today, even if I had some serving problems,” he said.

“It was a challenge, I would have never dreamed six months ago about this kind of a comeback. It’s all just unbelievable.” The victory was the first for Isner against 2009 US Open winner Del Potro in four meetings. Isner had knocked out top seed Novak Djokovic in the quarter-finals.

Isner’s fourth career semi-final at the Masters 1000 level took nearly three hours, with the winner firing 23 aces and 63 winners.

Isner broke five times and committed 49 unforced errors.

Del Potro was playing his second Cincinnati semi-final after reaching the final four in 2012. The 24-year-old old Argentine owns two trophies this season on the ATP, but missed the chance to reach his 23rd final.

Del Potro scooped up the first set in a tiebreaker and looked to be cruising to a quick win in the second before his slow collapse.

After getting his reprieve on the failed match point, Isner began to grind, winning the second set in 71 minutes on his fifth set point. Isner made a third-set breakthrough with a 2-0 lead. He reached his first match point with a concluding ace and took the win as Del Potro hit the net with a return.

“I can’t believe I’m in the final,” Isner said. “The crowd really helped me. Ever after his match point, I knew it wasn’t over until it was over.

“I just told myself to keep fighting.” In the women’s event, Serena Williams and Victoria Azarenka, the WTA top two, will battle for that trophy after difficult wins.

Williams needed a pair of comebacks to overcome defending champion Li Na of China 7-5, 7-5, reaching her first final at the event.

Second seed Azarenka emerged the winner in a contest riddled with 23 breaks of serve, including the first six games.

She finally beat 14th seed Jelena Jankovic 4-6, 6-2, 6-3.

Williams is playing one of the few events she has not won. Her previous best at the venue was a 2006 semi-final.

“When you win a lot you develop a lot of confidence and a belief that you can do well,” said the 31-year-old who has won 15 titles in the last 16 months and is going for her ninth of the season.

“I’ve been training more and enjoying it a lot over the past year and a half.” Li lost on when she struck a double-fault on match point.

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