TORONTO, Canada (AFP) - Defending champion Novak Djokovic progressed into the last eight of the Toronto Masters on Thursday with a 6-4, 6-4 win over Sweden's Robin Soderling.

Croatian tenager Marin Cilic spring an unwelcome surprise on sluggish Andy Roddick, taking down the former US Open winner whose game is in crisis, 6-4, 4-6, 6-4.

"Something doesn't feel comfortable," said the American who broke a racket after a dispute with the chair umpire concerning an over-rule which the official later admitted he got wrong.

"I keep feeling if I get a couple three, four matches into a tournament I'll be all right," said Roddick, playing for the first time since an early Wimbledon exit.

"I'm not able to do that. It was pretty ordinary out there today. Things are going wrong a little bit across the board. The forehand is just not doing anything, I'm missing it.

"That's the one that I need to click right now."

Serbian world number three Djokovic is struggling to keep pace with Rafael Nadal, the world number two who is closing in on Roger Federer on top of the rankings.

Nothing can happen at the summit this week.

But Nadal currently stands 770 points behind Federer who suffered a shock second round defeat to France's Gilles Simon on Wednesday as he played his first match since losing his Wimbledon title.

The Spaniard could cut that margin to a mere 275 should he win the title on Sunday for a second of his career in Canada.

"I played the best tennis of my career in the first six months of the year," said Australian Open champion Djokovic.

"I just want to care and keep my focus about my career. If I continue going forward the same way, the results will come."

Simon followed up his win over Federer by clinching his eighth victory in a row on Thursday also to reach the quarter-finals.

The world number 22, who lifted the Indianapolis title four days ago, stopped Argentine Jose Acasuso 6-3, 6-4.

"I can't just stay on this match," he said. "It was the same for my victory in Indianapolis.

"I didn't have the time to enjoy it yet, but it's a good thing for me. If I lose this week, then I think I'll make a big party for all these reasons."