In the afternoon session, Federer celebrated his place at the World Tour Finals in London with a 6-3, 6-4 victory over Germany's Kohlschreiber as the former world number one continues his return to form.

He now meets Argentine Del Potro, who defeated rising Bulgarian star Grigor Dimitrov 3-6, 6-3, 6-4 in a high quality encounter on court one.

"It was a complicated match because he can hit the ball with lots of lift but also very flat," explained Federer.

"He hit a few double faults at important moments so I was a bit lucky too," the Swiss 17-time Grand Slam winner said.



The 32-year-old said the matchup with Del Potro was "an important match for both of us.”

With the World Tour Finals coming up “it could give one of us an advantage for London so it's a key match,” he said.

"I like to play him, he's one of the best indoor players on the Tour and has been playing really well,” he said.



“I hope he's maybe a bit tired because I'm tired too," he joked.

Djokovic, who won in Paris in 2009 and is not only chasing a 40th ATP title but also the world number one spot, dropped the first set before storming back for a 6-7 (5/7), 6-1, 6-2 victory over American John Isner.

He now meets Wawrinka against whom he has already played some classic matches this season, notably their five-set semi-final at the US Open where the Serb finally prevailed.

"It is a big challenge for me and both Wawrinka, also," said Djokovic who also has the Davis Cup final to consider on November 15th.

"It's not the first time I'm playing against him at this stage of a tournament,” he said.

“It's not best of five, so we will not go the fifth set," he said in reference to their US Open epic.

"You know, whenever we play each other it's long exchanges, you know, very tough match mentally, physically,” Djokovic said.

“But I'm ready for it,” he said.

"He has been enjoying probably the best season in his career and he has one of the best one handed backhands in the world.

"He just feels more confident than he ever was."

Seventh-ranked Wawrinka booked his ticket for London when he comfortably defeated Spaniard Nicolas Almagro 6-3, 6-2.

When asked prior to the Djokovic match who he might prefer in Friday's quarterfinals, he admitted Djokovic was the man he wanted.

"If I do have a preference it would be Novak because we've had some great matches in the past,"

Spain's Ferrer showed little mercy against Frenchman Gilles Simon and by converting three of six break points, that was the difference as he stays in the hunt for a third ATP title this season, following Auckland and Buenos Aires.

His defence continues on Friday with a last eight tie against sixth seed Tomas Berdych, from the Czech Republic, who beat Canada's Davis Cup semi-finalist and 10th seed Milos Raonic in a match that ended Raonic's London hopes.

France's Richard Gasquet, who has also qualified for the World Tour Finals, takes on Japanese world number 18 Kei Nishikori for the right to play world number one Rafael Nadal or last year's surprise finalist Jerzy Janowicz of Poland in the last four.