Novak Djokovic of Serbia reacts after hitting a return to Sergiy Stakhovsky of Ukraine during their men's singles match at the Dubai Tennis Championships February 29, 2012.  [Photo\Agencies]

DUBAI - Holder Novak Djokovic had to combat Sergiy Stakhovsky's aggressive serve and volley game to reach the Dubai Championship quarter-finals on Wednesday, and next faces a baseline barrage from compatriot Janko Tipsarevic.

World number one Djokovic overcame the Ukrainian 7-6 6-3 to improve to 9-0 for the year.

"I was expecting a lot of serve and volley attacks, especially after first serve," said Australian Open champion Djokovic. "He was using it really well, making my return games very difficult."

The Serb must now adjust to counter Tipsarevic, who battled past Italy's Flavio Cipolla 6-7 6-1, 6-1.

"[Janko's] very solid from the baseline," said Djokovic. "When he has time and he steps into the court, he's very dangerous. I need to try to be aggressive. I need to try to stay close to the line. That's all. He doesn't have many weaknesses in his game."

Second seed Roger Federer produced his usual array of exquisite shotmaking to down Feliciano Lopez 7-5 6-3 and set up a last eight meeting with Mikhail Youzhny after the Russian ousted American sixth seed Mardy Fish 6-2 7-6.

"It was difficult. I've obviously played Feliciano many, many times way back and now on tour as well, but I've never played him when he was ranked so high and potentially so confident," former champion Federer said of his victory which took his record to 10-0 against the Spaniard.

"I just tried to focus on my serve, made sure from that end I wasn't doing any stupid stuff, and at the end I got a bit of a read on his serve.

"Those are the kind of matches you need early on in a tournament to feel good about how you're handling those tough moments."

World number four Andy Murray eased past Swiss qualifier Marco Chiudinelli 6-3 6-4 and now takes on Czech Tomas Berdych, who he has not beaten since 2005.

Berdych said his head-to-head record agaist the Scot, which he leads 3-1, counted for little.

"The statistics are one thing, and what's going to happen on court is the other one," said the world number seven.

The last quarter final pits Juan Martin Del Potro, a winner last week in Marseille, against fourth-seeded Frenchman Jo-Wilfried Tsonga.

Del Potro eased past Kazakhstan's Andrey Golubev 6-4 6-2 while Tsonga beat Czech Lukas Rosol 6-3 6-4.