Djokovic ups his game with quick Basel win

Djokovic, who had to struggle in his opening match over three sets, was absolutely untroubled by the Polish qualifier ranked 64th in the world, going through to the quarter-finals in just 54 minutes.

"Today was a really comfortable match," said the world number one. "I felt good on court. I'm happy to be playing better.

"This was the goal, I expected that I would struggle with rhythm after not playing for six weeks. But I have no complaints with my game.

"It was a good performance and I'll try to do better tomorrow (Friday)."

Djokovic lifted his impressive 2011 record to 66 wins and three defeats as he won again after overcoming a back injury that he called the worst of his career.

"I'm not 100 percent and to be honest I don't expect to get there this week, I would be surprised if I did. I only started serving a few days before my first match and I could tell I was lacking rhythm on second serve. But it was getting better today.

"I need to stay positive and increase the rhythm and intensity of each match."

Champion in 2009 and a losing finalist against Roger Federer in 2010, Djokovic will now face Cypriot Marcos Baghdatis, who booked his last eight ticket on Wednesday.

Elsewhere on Thursday, seventh seed Andy Roddick lost serve three times in the first set but recovered to put out Czech Radek Stepanek 2-6, 6-3, 6-3. The victory moves Roddick into a quarter-final with four-time champion Roger Federer.

The pair last met in the semi-finals here a year ago with the Swiss winning in straight sets. The quarter-final will be their fourth meeting in Federer's hometown since 2001.

"It is what it is," Roddick said of the contest. "There won't be any surprises, neither of us are likely to worry. It will be about who executes better."

In-form Florian Mayer followed up a third-round upset of Rafael Nadal in Shanghai with a 6-3, 6-1 defeat of Ivan Ljubicic.

"I'm surprised by this win, but I have so much confidence from beating Nadal. I know on my best game I can defeat anyone," said 22nd-ranked German Mayer.

Japan's Kei Nishikori continued his Shanghai momentum after a run to the semi-finals in China.

The 21-year-old, who stands as Asia's best-ranked player with a 32nd ranking, easily overcame Italian Andreas Seppi 6-3, 7-6 (7/4).

The week ended early for American James Blake, with the 31-year-old exiting at the hands of Mikhail Kukushkin 6-3, 6-4.