Rafael Nadal survived a fierce assault from Stanislas Wawrinka to reach the Shanghai Masters semi-finals Friday, staying on course for a potential title match against Novak Djokovic, who recovered from a set down to also claim victory.

World number one Nadal was pushed to the limit by Wawrinka in a highly competitive first set, but the relentless Spaniard came out on top in a gripping tie-break lasting more than 20 minutes.

It was one-way traffic in the second set as he prevailed 7-6 (12/10), 6-1.

Top seed Djokovic kept his side of the bargain under floodlights at the Qizhong Tennis Center, withstanding a feisty challenge from Frenchman Gael Monfils to win his quarter-final 6-7 (4/7), 6-2, 6-4.

Elsewhere in last-eight action, Jo-Wilfried Tsonga and Juan Martin del Potro breezed through their matches in straight sets as they hunt berths at next month's elite World Tour Finals

Nadal, who has won 10 titles -- including the French Open and US Open -- this year, fended off three set points for Wawrinka, against whom he now boasts an 11-0 record, before taking his fourth opportunity to win the opener.

A dispirited Wawrinka ran out of steam in the second set against never-say-die Nadal, who regained the number one ranking this week and is chasing a record sixth Masters title in a single season.

Earlier, Monfils and Djokovic swapped two service breaks each before the match settled into a more regular groove, going to a tie-break won by the Frenchman when the top seed went long with a backhand.

But Monfils, cutting an imposing figure in his bright orange top with a shock of dark hair, let his intensity slip at the start of the set and Djokovic immediately seized the initiative with a break.

A time violation against Monfils rattled the Frenchman, who became embroiled in an argument with the umpire and was soon flat on his back receiving treatment on his abdominal muscles as the set slipped away from him.

Monfils, who conquered Roger Federer in the previous round, re-discovered his mojo at the start of the decider, rattling Djokovic.

But it was the Serb who made the crucial break, letting out a roar of triumph before going on to seal the match after an absorbing two hours and 22 minutes.

"Inexplicably I started serving quite badly, but not many unforced errors," said Djokovic. "It happens. I mean, I was preparing for this match as well as I prepare for every other. It's just sometimes that you start off slowly and you're not feeling the ball as much."

"Today was a very physical match and very intense," he added. "Both of us, we played many rallies. I knew coming into the match that he's going to run for every ball and he's going to make me play an extra shot."

Earlier, Argentine sixth seed Del Potro, fresh from winning the Japan Open, eased into the semi-finals, firing 27 winners and making just eight unforced errors in a routine 6-3, 6-3 win against Nicolas Almagro, the Spanish 15th seed.

Del Potro, 25, just one win away from qualifying for the World Tour Finals, is wary of his semi-final match-up against Nadal, describing him as "unbeatable".

"You have to have a perfect day with Rafa. We'll see how it's going," he said.

Seventh seed Tsonga, 28, who admitted he was not quite 100 percent fit after problems with his knee, which forced him to miss the US Open, was equally impressive, beating 50th-ranked Florian Mayer of Germany 6-2, 6-3 in just 64 minutes.

The top eight players of the season qualify for the World Tour Finals in London, with five places still up for grabs. Nadal, Djokovic and David Ferrer have already qualified.

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