Indian Wells, USA, 18 March 2012 | AFP

Hard-serving American John Isner’s memorable run continued as he stunned world No.1 Novak Djokovic to book an Indian Wells final showdown with world No.3 Roger Federer.

Isner fired his 20th ace of the match to topple the top seed and defending champion 7-6(7) 3-6 7-6(5) on Saturday.

Federer then unleashed an ace on match point to seal a 6-3 6-4 victory over world No.2 Rafael Nadal as the two renewed their epic rivalry with their first meeting at the Indian Wells Masters.

Isner’s first victory over a world No.1 ensures he will move into the top 10 for the first time on Monday.

“Not many people can say they’ve ever beaten the No.1 player in the world,” said the 26-year-old American. “I’ll always be able to say that.

“I’m just going to keep on riding this wave I’m on and see how far it can take me.”

For Djokovic, 24, it marked a second straight semi-final defeat after he fell at the same stage in Dubai to Andy Murray.

The reigning Australian, US and Wimbledon champion is 14-2 in 2012.

“It’s frustrating when somebody serves over 70 per cent of the first serves in and with that angle and with that speed and accuracy,” Djokovic said.

Djokovic saved a match point in the 12th game of the third set and two more on his own serve in the deciding tiebreaker before Isner closed it out after two hours, eight minutes.

One of the sport’s great rivalries was on display in the second semi-final between 16-time grand slam winner Federer and reigning French Open champ Nadal which started three and a half hours late and was played in difficult windy and rainy conditions.

“I had a good day. It was a great match in tough conditions,” Federer said. “It was so difficult but, man, I couldn’t be more happy. I played amazing.

“We both expected rain, and it did rain a few times.”

Federer even had a few extra minutes to think about what turned out to be his final ace after officials pulled the players off the court because of rain just as he held match point leading 5-4 and 40-30.

He returned a few moments later and hammered the final nail in the coffin – a 201km ace that ended the one-hour, 31-minute match.

“I thought about going down the ‘T’ but, when I was tossing the ball in the air, I thought I would go the other way,” he said.

Nadal and Federer had met 27 times previously but never before on the hardcourts at the Indian Wells Tennis Garden.

Nadal has the edge over his Swiss foe having won 18 times, including four of the past six.

This marks their second meeting this year after Nadal beat Federer in the semifinals at the Australian Open.

Nadal said he couldn’t overcome Federer’s quick start on Saturday and then the wind and rain on centre court troubled him.

“He started the match playing unbelievable,” Nadal said. “At the beginning, it wasn’t windy and I was able to play with some tactics.

“But later, the crazy wind started and it was difficult for me to play.”