Defending champion Novak Djokovic progressed into the last eight of the Toronto Masters with a 6-4, 6-4 win over Sweden's Robin Soderling.
Croatian teenager 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.