MELBOURNE, Australia — Rafael Nadal and Andy Murray held off two of the tallest men and biggest servers in tennis early today to set up a quarterfinal meeting at the Australian Open.

Defending champion Nadal had a 6-4, 4-6, 6-4, 6-4 win over 6-foot-10 Ivo Karlovic of Croatia, the tallest man on the tour.

In the previous match on Rod Laver Arena, No. 5 Murray overcame 6-foot-9 American John Isner 7-6 (4), 6-3, 6-2. Murray hasn’t dropped a set in four matches.

Over at Hisense Arena, Nadia Petrova advanced with another upset win, beating third-ranked Svetlana Kuznetsova 6-3, 3-6, 6-1 to reach the quarters.

In the other section of Petrova’s half of the draw, Zheng Jie set another national mark by becoming the first Chinese player to reach the quarterfinals at Melbourne Park with a 7-6 (6), 6-4 victory over Alona Bondarenko.

Murray, a 22-year-old Scot, rated Isner’s serve among the best in the game, so he was delighted to wear down the American after a crucual service break in the eighth game of the second set. He fended off break points in the next game to serve out the set.

“It’s tough. I had my coach serving at me from the service line this morning to try to get used to it,” Murray said of the 6-foot-9 Isner’s serve. “But once you get out there it’s kind of tricky.”

Murray broke serve again in the seventh game of the third set when the American netted a forehand and then smashed his racket into the court in disgust.

“It’s been good. I moved really well since the start of the tournament,” Murray said. “I didn’t drop a set yet . . . not too much to complain about.”

So far. The loss was Isner’s first of the year, which started with his first career ATP title at Auckland 10 days ago.