Ivo Karlovic has been the thorn in Novak Djokovic’s side once again after he knocked the Serbian star out of the Qatar Open in the quarter-finals.

Djokovic was looking in formidable form in the competition and his rivals would have been somewhat concerned by the world number one’s start to 2015.

However, Karlovic has given a Djokovic another reality check, having beaten him for the second time in his career, with a 6-7 (2-7) 7-6
(8-6) 6-4 victory.

Karlovic was ruthless with his serving throughout the contest and Djokovic failed to cope, as the underdog hammered down 21 aces, in what were admittedly difficult conditions with high winds affecting proceedings.

Djokovic did have opportunities during the contest to send the Croatian out of the competition in Doha and was twice within two points of winning the match in the second set tie-breaker.

However dropping serve in the seventh game of the deciding set was Djokovic’s undoing as Karlovic now looks ahead to what will be another stern test in the form ofDavid Ferrer in the semi-finals, after the Spaniard saw off Germany’s Dustin Brown 6-2 6-2.

The 35-year-old Karlovic was delighted with the victory and was pleased with how he coped better with the conditions than his opponent.

He said: “I was feeling good despite the wind. I know he wasn’t able to show his full range.

“I was relaxed and didn’t feel I had to do anything extraordinary. I just had to focus on my game.”