World number one Andy Murray claimed his 26th consecutive victory on Wednesday with a battling 7-6 (8/6), 7-5 win over Austria's Gerald Melzer to reach the Qatar Open quarter-finals.

He was joined in the last-eight by second seed Novak Djokovic who eased past Horacio Zeballos 6-3, 6-4 in just 72 minutes before being stunned by his Argentine opponent's request for a selfie of the pair on court.

"Making a selfie, that's the first time I have had this experience in my career," said Djokovic. "Horacio -- well done, very original."

Murray's 2 hour 23 minute match proved the most exciting of the evening though, and possibly the whole tournament so far.

In a 78-minute first set, Melzer, playing some inspired tennis, saved eight set points before eventually succumbing in a hard-fought tie-break.

The pair traded baseline passing shots, with Melzer the world number 68, matching Murray and looking like he could bring the world number one's winning streak to an end.

As the match wore on, Murray looked increasingly frustrated by his own game and some of the line calls.

"I was a bit lucky to get through," said Murray. "He played great, great tennis, he was winning large parts of the match."

He added: "It was a really good match. I was happy with how I handled it.

"It wasn't easy because I was having to do a lot of defending and I wasn't able to impose myself as I would've liked.

"But the positive was in the important moments I stayed strong."

Murray will play Spain's Nicolas Almagro in the last eight. Almagro beat Germany's Philipp Kohlschreiber 7-6 (7/5), 7-6 (8/6).

Djokovic next faces 38-year-old Radek Stepanek after the Czech knocked out Belgium's Arthur De Greef, 14 years his junior, 6-3, 6-2.

Stepanek is a former Wimbledon quarter-finalist who turned professional in 1996, just four years after De Greef was born.

His victory means he is the oldest ATP quarter-finalist since a 42-year-old Jimmy Connors played in the 1995 Halle grass court event in Germany.

Stepanek said afterwards that he would continue playing for several years and "will be fighting Jimmy Connors" to make history.

The number three seed Tomas Berdych beat Czech compatriot Jiri Vesely 7-6 (7/5), 1-6, 6-1, to set up an intriguing clash with France's Jo-Wilfried Tsonga who blasted past Germany's Dustin Brown 6-1, 6-3 in less than an hour.

However, the number four seed, Belgium's David Goffin who beat Murray in an exhibition match in Abu Dhabi last week, is out losing 6-1, 7-6 (8/6) to Spain's Fernando Verdasco.