SHANGHAI (AFP) - Rafael Nadal and Novak Djokovic kept the excitement high at the Shanghai Open Thursday as the top-seeded pair booked into the quarter-finals with ease.

Nadal, vowing to overcome his semi-final crash last week in Beijing, did just that as he rousted Tommy Robredo 6-1, 6-4, achieving a 5-0 career record over his compatriot without the loss of a set.

"I'm playing well, really well, but I had two terrible games in the start of the second set," said Nadal. "That's what I have to improve if I want to win against the top players.

"Yesterday I had a similar thing. It can't happen tomorrow.

Djokovic was equally ruthless as he put out the last German, veteran Rainer Schuettler, 6-4, 6-2, completing the job with back-to-back aces.

"I've been working on physical strength and fitness a lot in the last couple of months, and it's been paying off," said Djokovic, who claimed the Beijing crown last weekend.

"It's playing one of the key roles in situations like this. When you are playing week after week, it's important to be physically strong, and that gives you an advantage over your opponents."

The event has been plagued by retirements, with two more on Thursday in the third round after earlier injury exits led by Andy Roddick and Juan Martin Del Potro.

Russia's Nikolay Davydenko beat Chile's Fernando Gonzalez to reach the last eight and move closer to securing a place in the ATP's season-ending final.

But the sixth-seeded Davydenko -- who beat the 10th seed Gonzalez, 6-3, 7-5 -- said he would not be heartbroken should he fail to qualify for the eight-man World Tour Finals in London, and would instead just enjoy the time off.

"Like my wife said already: 'You're already Top 15 this year. Why do you want to think about London?'" he told reporters.

"I'll enjoy a holiday if I don't reach London. You can lose your mind worrying and lose in every tournament in the first round.

"If I don't reach London, it's good. I have more time to spend with my family and then... prepare for next season. It's been a long season," he said.

Davydenko is currently battling for a spot in the November 22-29 tournament along with a potential 11 other players, including Roddick, Jo-Wilfried Tsonga, Fernando Verdasco, Fernando Gonzalez, Robin Soderling and Gilles Simon.

Roger Federer, Nadal, injured Andy Murray, Djokovic and Del Potro have already qualified.

Two French seeds were knocked out as Roland Garros finalist Soderling beat frustrated number five Tsonga 6-3, 6-3.

The Swede produced 23 winners and set up three match points with his eighth ace, advancing in 58 minutes over the winner of last week's Tokyo title.

The 11th seed Gael Monfils lasted only 37 minutes before quitting injured to hand a 6-2, 3-0 win to Croatian veteran Ivan Ljubicic.

Monfils was affected by back pain and has struggled on occasion in recent weeks.