Julia Goerges booked the first of the semifinal spots defeating Russian Anastasia Pavlyuchenkova as Novak Djokovic equalled Ivan Lendl's 1986 record of a 29-0 winning start to a season on Thursday when he reached the Madrid Masters quarterfinals.

The Serb second seed cruised to a 6-1, 6-2 thrashing of Spaniard Guillermo Garcia-Lopez which took less than an hour to extend his overall winning streak to 31, stretching back to the two Davis Cup final singles he won in December.

The record for a winning start to a season remains 42 matches, set by John McEnroe in 1984, with Bjorn Borg, who had 33 straight wins in 1980, in second spot.

"I was winning my service games really comfortably and that's something that I'm happy about, it's a very encouraging fact for my upcoming matches," said Djokovic.

"It's important for me to see that I raised the level of performance today for the quarter-finals."

Goerges, who is set for a move into the ranking Top 25 on Monday, took just under 90 minutes to clock her ninth straight victory, a run which began when she claimed the Stuttgart title a fortnight ago.

Goerges, 22, was the first German to lift home honours in Stuttgart since Anke Huber in 1994. Along the way, she accounted for world number one Caroline Wozniacki, her third-round victim this week in Madrid as well.

Goerges, who saw off Wozniacki in the Stuttgart final last week, enjoyed a 6-4, 1-6, 6-3 win over the world number one to set up the quarterfinal outing against Anastasia Pavlyuchenkova, who upset Stosur 7-6 (7/4), 6-3.

Goerges saved six break points against Pavlyuchenkova and broke the Russian three times, going through on the first of three match points to end it 6-4, 6-2.

She next faces the winner form fourth-seeded Victoria Azarenka of Belarus or Czech Lucie Safarova.

Goerges, an Auckland semifinalist in January, improved to 22-9 this season and leads the WTA with 16 victories on clay in 2011.

Top-seeded holder Rafael Nadal went through to the last eight without lifting a racquet as opponent Juan Martin Del Potro retired before their third round match with hip pain.

Unseeded Del Potro, the 2009 US Open champion, who is making a recovery this season after missing more than eight months of play in 2010 after wrist surgery, had been bothered by the problem since reaching the Estoril semi-finals at the weekend.

"I have experience with injuries, and I decided not to play," Del Potro said as he prepared to fly home to Buenos Aires for medical checks.

The Argentine will not play the Rome Masters starting on Sunday and could well be in doubt with the French Open starting on May 22.

"The pain was very strong," said the Argentine.

Third seed Roger Federer got past Belgian Xavier Malisse 6-4, 6-3 after a late-night struggle on Wednesday against Feliciano Lopez which went three hours.

"It was a quick turnaround," said the two-time champion. "Mentally it was tough, I had to be ready to play a different kind of match (from the night before).

"I didn't have high expectations, I just wanted to play a good match. I was able to do that."

Thomaz Bellucci profitted from his first meeting with Scot fourth seed Andy Murray, securing a 6-4, 6-2 win in 90 minutes.

Murray's temper boiled over with the seed warned for audible obscenbities from early on in the proceedings as Bellucci won the last four games to advance to the last eight.

But the British player wasn't too downhearted with his form.

"I've got to look more at the week as a whole, I was coming back from an injury that wasn't serious but an elbow injury isn't easy for tennis players," said Murray.

"You need to be quite cautious and not do too much too soon because then you take a step back, but I think I've judged it pretty well."

Fifth seed Robin Soderling, twice a Roland Garros finalist, defeated slumping Frenchman Jo-Wilfried Tsonga 7-6 (10/8), 7-5.

In the other women's events, French Open champion Francesca Schiavone and Roland Garros runner-up Samantha Stosur also went out.

America's Bethanie Mattek-Sands defeated third seed Schiavone 7-6 (7/5), 6-3 but there were no problems for fourth seed Victoria Azarenka who overcame Spain's Arantxa Parra Santonja 6-0, 6-3.

Sixth seed Li Na of China, the Australian Open finalist, moved into the last eight thanks to a 2-6, 6-2, 6-1 win over Italian Roberta Vinci, who won in Barcelona last week.

"The first set was good for her, then I started thinking about hitting it more to her slice backhand," Li said.

"After Melbourne I wasn't winning any matches, so it's exciting I've now won three matches on clay. Things are going fantastic. Since my new coach joined my team I'm happier. I have more good energy now."