Top seed and defending champion Novak Djokovic rallied to see off Frenchman Gael Monfils 6-7(4) 6-2 6-4 in the quarter-finals of the Shanghai Open Friday.

The Serb, who lost his world number one ranking to Rafa Nadal on Monday, defeated Monfils, conqueror of Roger Federer in the previous round, in a match that last two hours and 23 minutes.

After twice exchanging breaks during the first set, the Frenchman bagged the tiebreak 7-4 to go ahead. But Djokovic fought back, twice breaking Monfils, who had to receive treatment on a stomach muscle.

Djokovic got the crucial break in the seventh game of the third set and closed out the match to set up a semi-final clash with another Frenchman Jo-Wilfried Tsonga.

Juan Martin del Potro kept his errors to a minimum as the Argentine breezed past Spain's Nicolas Almagro 6-3 6-3 to march into the semis.

Del Potro, seeded sixth, had also defeated Almagro in last week's Japan Open semi-finals and now needs one more victory to seal his spot for the season-ending ATP World Tour Finals in London next month.

The Argentine, who was suffering from fever during the earlier stages of the hard-court tournament, committed just eight unforced errors during his win and faced a single break point, which he went on to save.

"I played very well today, very solid," del Potro told reporters. "I played aggressive. I hit my forehand very well.

"I like the way I played today. I just want to keep improving (and) keep going far in this tournament."

Tsonga also took a positive step towards confirming his spot for London with a comfortable 6-2 6-3 win against German Florian Mayer.

World number three Andy Murray's withdrawal from the Tour Finals due to injury has meant anyone finishing ninth or better in the race to London will qualify for the prestigious season-ending tournament.

Spain's Nadal, who last week lost to Djokovic in the China Open final, faces Swiss Stanislas Wawrinka in the final last-eight clash on Friday.

(Reuters Quotes)