BEIJING - Novak Djokovic churned towards Rafael Nadal's all-time record for unbeaten starts to a tournament as he demolished Chinese number one Zhang Ze in less than an hour in Beijing on Thursday. The world number one showed no mercy to Zhang, ranked 219, in front of his home fans as he ended local hopes 6-2, 6-1 in 55 minutes to reach his sixth China Open quarter-final.

Djokovic, unbeaten in five appearances, now equals Jimmy Connors with 26 wins at a tournament before suffering a single defeat, in sight of Nadal's record of 31 at the French Open. "I guess as I keep coming back each year with that positive record, obviously gives me more confidence knowing that I played so well in the past on this court," he said.

"I just keep on going. That's all. There is no particular reason. There's a few things that play in my favour." Zhang, 25, could only applaud after he was outclassed in all facets by the Serbian 10-time Grand Slam-winner, who has only ever dropped three sets at the China Open. "As for his level of play, his game, I think there's no loopholes or shortcomings. Actually, I prepared very well in order to play my game. But he won three major titles (this year)," said Zhang. "His performance is amazing. He is really good."

Earlier Ivo Karlovic bludgeoned his way into the record books for career aces, and Garbine Muguruza had an eventful 22nd birthday as she smashed a racquet, reached the WTA Finals and then celebrated with cake. Muguruza was frustrated by Croatia's Mirjana Lucic-Baroni but she gathered herself for a 1-6, 6-2, 6-1 win which qualified her for the glitzy, eight-player season finale in Singapore.

"I'm just really motivated, like I said before, to try to finish good. It's great to be qualified. But tomorrow I have another match," said the Spaniard, who was presented with a cake on court after the win. The day's most historic achievement came from Karlovic, who broke Goran Ivanisevic's record for career aces as he went down to Uruguay's Pablo Cuevas.

The 6ft 11ins (2.11m) Karlovic hammered 26 aces in his 7-6 (7/5), 7-6 (9/7) defeat, reaching a total of 10,247 and surpassing compatriot Ivanisevic's 10,237 along the way. The record was consolation for Karlovic after his loss to 37th-ranked Cuevas, who is enjoying a dream run in Beijing after he beat world number five Tomas Berdych in the first round.

Last month's US Open finalists both also suffered upsets with New York winner Flavia Pennetta going out 3-6, 6-4, 6-3 to Anastasia Pavlyuchenkova. Pennetta's defeat came after fellow Italian Roberta Vinci was beaten 6-1, 3-6, 6-2 by Bethanie Mattek-Sands, in yet another surprise at the unpredictable Beijing tournament. In the late match, Ana Ivanovic outlasted Svetlana Kuznetsova 7-5, 4-6, 6-2 to set up a quarter-final with Pavlyuchenkova despite needing repeated treatment for a back problem.