* Djokovic sets up Murray semi with win over Tipsarevic
* Murray overcomes knee problem against Berdych
* Federer maintains unbeaten record against Youzhny (Updates with Del Porto win)
By Matt Smith
DUBAI, March 1 (Reuters) - World number one Novak Djokovic beat fellow-Serb Janko Tipsarevic 6-1 7-6 in the quarter-finals of the Dubai Tennis Championships on Thursday to set up a meeting with Andy Murray in the last four.
Murray, who wasted six match points and overcame a knee injury to beat Tomas Berdych 6-3 7-5, faces Djokovic for the first time since the Serb triumphed in a five-set epic in the Australian Open semi-finals in January.
Roger Federer is also through to the semi-finals after beating Mikhail Youzhny 6-3 6-4 and will face Argentine Juan Martin Del Potro, who beat France’s Jo-Wilfried Tsonga 7-6 6-2, on Friday.
Djokovic, seeking a fourth straight Dubai title, bullied Tipsarevic from the outset, breaking to go 3-1 ahead in the first set of their night encounter.
Tipsarevic, ranked a career-high ninth in the world, put up little resistance, netting a lazy backhand to give Djokovic a double break and an unassailable 5-1 lead.
He made a better fist of the second set, matching Djokovic’s pounding groundstrokes in a series of ferocious rallies from the baseline.
Yet the bespectacled Tipsarevic remained erratic. Serving at 2-2, he dispatched three aces and two double faults in the space of six points as he eventually held.
The set went to a tiebreak. Tipsarevic, serving second, went 3-0 up with a brilliant forehand winner down the line.
Djokovic came back to level at 4-4, but a mishit gifted Tipsarevic a set point on serve. The 27-year-old’s demons returned as he made another double fault and Djokovic eventually saw out the match with a forehand winner to clinch the tiebreak 8-6.
”It was a very tense second set,“ Djokovic said in a court-side interview. ”Towards the end, we both had chances and both got quite nervous and made some unforced errors.
“We’ve known each other for a very long time and there are no secrets. We’re very good friends, but we’re both professionals.”
Murray, who went into his match with a 3-1 losing record to Berdych, appeared to be cruising at one set up and 2-0 ahead in the second.
However, with the Briton’s movement becoming increasingly laboured, Berdych levelled at 3-3 as both players hugged the baseline on a soporific centre court, the stands barely half full and temperatures topping 30 degrees Celsius.
The Czech was on top but Murray dug in and broke once more, playing a forehand cross-court shot from wide of the tramlines that Berdych had no reply to for a 6-5 lead.
Murray, 24, wasted six match points on serve, but he eventually triumphed when Berdych put a forehand long.
“I had a problem with it (the knee) since Brisbane and it’s come and gone,” Murray told reporters.
“It was a bit sore right before the tournament. I didn’t feel it at all in the first couple of matches, and then right at the beginning of the second set I felt it.”
World number three Federer had beaten Youzhny in all their 11 previous meetings and his winning streak never looked in danger after the Russian went 3-1 behind in the first set.
Federer saw out the first set with a fierce serve the ailing Youzhny could only club long.
The Russian, who has slumped to 34th in the world from a career-high eighth, played another poor forehand to lose his serve on the opening game of the second set, effectively ending the contest as Federer, a 16-times grand slam winner, served out. (Editing by John Mehaffey)