Shanghai, China (My Sportsbook) - Australian Open champion Rafael Nadal and last week's Beijing titlist Novak Djokovic were a pair of quarterfinal winners Friday at the $5.25 million Shanghai ATP Masters.

The top-seeded and former world No. 1 Nadal was tied with former top-10 star Ivan Ljubicic 3-6, 6-3 when the big Croat retired from the bout after two sets due to a left hip problem.

Six other players quit with a variety of ailments this week, as U.S. Open champion Juan Martin del Potro, Wimbledon runner-up Andy Roddick, French slugger Gael Monfils, Germans Tommy Haas and Mischa Zverev, and Argentine Jose Acasuso also exited the draw via retirements. World No. 1 superstar Roger Federer and No. 3 Andy Murray had already pulled out of Shanghai before the event commenced.

The six-time major champion Nadal will face fellow lefthander and fellow Spaniard Feliciano Lopez in Saturday's semifinals. Lopez upset ninth-seeded French Open runner-up Robin Soderling 7-6 (7-4), 6-3 on Day 6.

A second-seeded Djokovic managed to hold off eighth-seeded Frenchman Gilles Simon 6-3, 2-6, 6-2 in 2 hours, 23 minutes on the hardcourts at Qi Zhong Tennis Center, the former site of the ATP's Tennis Masters Cup, which Djokovic captured last year. Djokovic and Simon combined for 11 services breaks, including six for the winner from Serbia.

The hot Djokovic is fresh off his hardcourt title last week in Beijing, while Simon titled in Thailand two weeks ago.

Djokovic's semifinal opponent will be sixth-seeded Russian star Nikolay Davydenko, who got past 13th-seeded Czech Radek Stepanek 6-1, 4-6, 6-1.

This inaugural tournament closes out a three-week Asian swing on the ATP and the winner will take home $616,500. It serves as the penultimate Masters event, with the last one coming in Paris next month.