DOHA, Qatar (AP) — Defending champion Novak Djokovic and top-seeded Andy Murray posted straight-set wins on Wednesday to reach the Qatar Open quarterfinals, but only Djokovic was asked to pose for a selfie by his opponent after the match.

Djokovic, a 12-time Grand Slam champion, honored the unusual request of Horacio Zeballos of Argentina after his 6-3, 6-4 win.

"I just have to mention making a selfie after the match was over, that was the first time that I ever had this kind of experience in my career," Djokovic said on the court. "So, Horacio, well done. Very original."

Murray had a challenging outing against Gerald Melzer of Austria, the younger brother of former world No. 8 Jurgen Melzer, before advancing to the quarterfinals with a 7-6 (6) 7-5 win.

"He played great, great tennis and was dominating large parts of the match," said Murray, who was on the defense through much of the match. "He made it extremely, extremely difficult. I was a bit lucky to through in two sets today.

"I think he's playing much better than someone ranked 69 in the world," Murray added.

In the first set, Murray required nine set points before Melzer mis-hit a forehand to surrender the set. In the second, Melzer saved two Murray match points on his own serve in the ninth game, and then broke for 5-5.

Murray broke Melzer's serve on a fourth break point in the 11th game and then sealed the victory on a third match point when Melzer blasted a shot long.

"Today was a perfect example of the depth in the men's games just now," Murray said. "I actually played pretty good, but he was hitting the ball huge from both sides. You need to be ready for every single match."

Murray, a two-time champion in Doha, will face Nicolas Almagro of Spain in the quarterfinals.

Djokovic never offered Zeballos a break point opportunity, but could only carve out one service break in each set against the Argentine's serve.

"Credit to Zeballos for playing some fearless tennis," Djokovic said. "He was stepping in and trying to go for his shots. He wasn't backing up to the baseline."

Djokovic will play qualifier Radek Stepanek of Czech Republic, in the quarterfinals.

At 38, Stepanek, who ranked a career-best No. 8 in July 2006, is the oldest ATP Tour quarterfinalist since a 42-year-old Jimmy Connors reached the final eight at the 1995 Halle tournament.

Stepanek defeated wildcard entrant Arthur De Greef of Belgium 6-3, 6-2 for his quarterfinal berth.

Spaniard Fernando Verdasco needed six match points, three in the second set tiebreaker, to upset fourth-seeded David Goffin of Belgium 6-1, 7-6 (6).

Verdasco will play sixth-seeded Ivo Karlovic of Croatia in the last eight.

The other quarterfinal will pit third-seeded Tomas Berdych of the Czech Republic against fifth-seeded Jo-Wilfried Tsonga of France, who beat Dustin Brown of Germany 6-1, 6-3.