The six-foot 11-inch, 35-year-old Karlovic, the tallest and oldest player on the main tour, won 6-7 (2/7), 7-6 (8/6), 6-4 to make the semi-finals.

Seven-time Grand Slam champion Djokovic often appeared affected by the conditions, especially with his ground strokes, but that did not prevent Karlovic hammering down another 21 aces, making 67 for the tournament so far.

That took him to within 12 of Andy Roddick's 9,074 aces, the second highest ever.

Djokovic was sufficiently exasperated to fling down his racquet in the second set and to sling it along the floor in the third, eventually settling for a smile and congratulations to Karlovic.

"I can't say if it was surprising or not, but he served very well," Djokovic said.

"But you could expect that. I was coming into the match knowing that I will have very, very few chances. I was hoping that these conditions and the wind would kind of give me some second-serve opportunities, but it didn't look this way."

The most crucial moments came at 3-3 in the final set when Djokovic saved one break point with a serve, volley and smash combination, but then slipped to break point down again by mistiming an inside-out forehand drive into the net.

Once again he made a good attempt to prevent the service break, landing a good serve and making a deep volley from a decent forecourt position only for Karlovic to launch himself sideways and pull off his best shot of the match, a spectacular running forehand pass down the line.

"In these particular matches, one ball can decide a winner, and that was the case," Djokovic said.

"I just played a little bit too defensive in that game. I thought I just, instead of kind of going through the ball, just sent the ball back.

"He made an unbelievable passing shot, hitting both lines in the corner and what can you say? That's all. The match was over."

- Nadal sympathy -

Djokovic nevertheless feels he still has a decent chance of winning the Australian Open for the fourth time in five years, especially as a doubles loss to Rafael Nadal later in the day left him free to fly to Melbourne earlier than expected.

The 14-times Grand Slam winner from Spain had himself suffered a stunning singles loss, in the first round, and afterwards made sympathetic noises.

"I don't feel better because Novak lost," Nadal said. "It's not going to make me play better tomorrow.

"It's the first tournament of the year and we both came here to do well, but that was not the case. Ivo played unbelievable in the last set."

Karlovic will now try to reach only the 13th final of his long career when he takes on David Ferrer, the fourth-seeded Spaniard in the semi-finals, feeling that he is fitter and more confident than for several years.

"I was feeling good even though it was windy," said Karlovic after his second career win over Djokovic, seven years after his last in Madrid.

"I know he wasn't able to show his full range (of shots) because of the wind.

"But I was relaxed and didn't feel I had to do anything extraordinary. I just had to focus on my game. So I guess I was luckier than him. But I am very happy that I won."

The tournament favourite is now Tomas Berdych, the former Wimbledon finalist, who outplayed a disappointing Richard Gasquet, the 2013 champion from France, by 6-2, 6-1.

"The conditions were not easy, but my plan to deal with the match worked well," said the third-seeded Czech who faces Italy's Andreas Seppi on Friday.

Seppi defeated Croatia's Ivan Dodig 7-5, 6-4 in his quarter-final.

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