World No.1 Novak Djokovic was buried by 21 aces as big-serving Croatian Ivo Karlovic clinched a 6-7 (2-7) 7-6 (8-6) 6-4 victory to reach the ATP Tour’s Qatar Open semi-finals on Thursday.

Top seed Djokovic joined second seeded Rafael Nadal on the sidelines in Doha after the Spanish star lost in the first round.

Djokovic appeared hampered by a stiff wind, which did not prevent Karlovic from hammering down the aces to take his total in three matches to 67 – but made it hard for the favourite to control his ground strokes.

Djokovic was nevertheless twice within two points of winning the match in the second set tie-breaker, before dropping serve in the seventh game of the final set. He never looked likely to make a break back.

“I was feeling good despite the wind,” said Karlovic. “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.”

Karlovic, the 35-year-old world number 27, claimed his second career win over the world number one having also triumphed at the Madrid Masters in 2008.

The six-foot 11-inch Croat, the tallest and oldest player on the main tour, will face Spanish fourth seed David Ferrer for a place in the final.