Gerald, the younger brother of former world No 8 Jurgen, played his part by handing the world No 1 a serious workout in two hours and 23 minutes.A passive Murray dropped serve twice in the opening set and world No 68 Melzer saved eight set points with some brave hitting before the Briton took the opener during an intense tie-break.He then got the break in the seventh game of the second set but failed to claim victory when serving at 5-4 as the 26-year-old left-hander Melzer forced a break of his own.When the 29-year-old Murray served for the match for the second time he made no mistake to extend his winning streak to 26 matches and stay on track for a third title in Doha.”He played great, great tennis,” Murray said of Melzer. “He was dominating large parts of the match and dictating a lot of the points and made it extremely difficult.”If he plays like that this year, he’ll climb higher up the rankings and I was lucky to get through in two sets today.”We’ve never practised or played against each other before and I told him if he keeps playing like that he’s going to get up there in the rankings. He’s playing much better than 69 in the world. He’s fairly young so he’s going to get better and better.”Murray felt his latest test was testament to the competitiveness of the men’s game, which he feels is getting harder and harder every year.”Today is a perfect example of the depth in the men’s game just now,” he said. “It was an extremely difficult match and I felt I played pretty good just now. I served well and was returning well, but he was hitting the ball huge from both sides. The depth is great now so you have to be prepared for every match.”The Wimbledon and Olympic champion will next take on Spain’s Nicolas Almagro after he upset seventh seed Philipp Kohlschreiber from Germany 7-6 (7-5) 7-6 (8-6).Second-seeded Novak Djokovic will face wily old Czech Radek Stepanek for a place in the last four after he beat Horacio Zeballos of Argentina 6-3 6-4.After the Serb won his match, his opponent asked him to pose for a selfie, and the 12-time Grand Slam champion cheerfully obliged.”I just have to mention that 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 court. “So, Horacio, well done. Very original.”Stepanek, 38, is the oldest ATP Tour quarter-finalist since 42-year-old Jimmy Connors reached the final eight at the 1995 Halle tournament after defeating wild-card entry Arthur De Greef of Belgium 6-3 6-2.Also, Fernando Verdasco needed six match points, three in the second set tie-breaker, to beat fourth-seeded David Goffin of Belgium 6-1 7-6 (8-6).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.