Djokovic books Semi final spot

Novak Djokovic book his US open semi final spot after Janko Tipsarevic was forced to retire in the later stages of their quarter final.

With Djokovic two sets to one and 3-0 up in the fourth set, when Tipsarevic, who was clearly struggling towards the end of the match, called it a day, meaning Djokovic progressed.

The world number one often wasn't at his best and frequently let his fellow Serb of the hook with unforced errors, which proved costly in the second set. However Djokovic still had enough in his locker to assert his dominance on the match before Tipsarevic's retirement at 7-6 (7-2), 6-7 (3-7), 6-0, 3-0.

In an entertaining first set which lasted 84 minutes, both players broke the others serve three times, with both Djokovic and Tipseravic failing to hold their serve when serving for the set. And so it went to a tie break, something the level and closeness of the tennis it deserved. However the world number one was simply to strong in a one sided finale to the opening set and eased to a comprehensive 7-2 tie break win.

Tipsarevic will no doubt looked to the failure to hold his serve when 6-5 ahead, gifting the Australian and Wimbledon champion three points in the game when he was well placed in the rally.

Tipsarevic certainly put the disappointment of failing to see out the first set however and came out of the traps quickest and flew into a 3-0 lead in the second, and had his chances to gain a double break 4-0 lead, however Djokovic defied his fellow Serb and stayed in the set. And with a certain sense of inevitability about it Djokovic broke back the very next game to bring the second set back to serve. The set followed serve all the way to a second successive tie break. This time Tipsarevic's threat didn't distinguish in the important game of the set, and at 3-2 to the lower ranked Serb, a clearly frustrated Djokovic gifted his opponent the first mini break of the tie break. A fired up Tipsarevic served brilliantly to engineer three set points, and Djokovic continued his error stricken game by hitting a simple chance long, to level the scores.

Despite his monumental effort to bring the game level, Tipsarevic was facing down the barrel in the third when Djokovic broke twice early on to take a dominant 4-0 lead. With Tipsarevic needing help from the physio, it was clear the set was over and Djokovic brought up three set points with a beautiful forehand down the line, however the dogid Tipsarevic prevented two of the three, only to double fault to gift Djokovic the third set 6-0.

After somehow managing to chase down a Tipsarevic drop shot and engineer a winner, the world number one recovered from a tricky position in the opening game of the fourth set, and went on to break Tipsarevic for a 2-0 lead. Djokovic followed Tipsarevic's suit by calling for a trainer early in the final set, however Tipsarevic was forced to retire just one game later, ensuring Djokovic continued his incredible run in 2011.

Djokovic will now face either of his last two grand slam semi finalists, in either Jo Wilfred Tsonga who he defeated on road to his Wimbledon crown, or Roger Federer who defeated the Serb in the French Open.