Murray made to sweat in quest to unseat Djoko as the World's No.1
Andy Murray survived a first-round scare at the Erste Bank Open in his bid to chase down World No.1 Novak Djokovic in the rankings.
The in-form Murray had won 24 consecutive sets before Slovakia's Martin Klizan took a tie-break off him in Vienna.
But the Wimbledon and Olympic champion cruised through the decider to win 6-3 6-7 (5-7) 6-0 in two hours and 22 minutes and set up a last-16 date with Frenchman Gilles Simon.
Murray admitted he had his sights on taking over top spot in the world rankings for the first time after back-to-back wins at the China Open and the Shanghai Masters.
But Murray - champion in Vienna two years ago - was troubled by an opponent he was meeting for the first time and who had missed a chunk of the season with a foot injury.
The World No.35 had three break points in the opening game, but Murray denied them all and went on to take the first set in 42 minutes.
Murray looked on course for victory when serving at 4-3 and then 6-5 in the second set.
But Klizan's ability to produce forehand winners saw Murray lose only his sixth tie-break out of 25 this year.
There had been some rare unforced errors in Murray's game, but they were eliminated in a one-sided third set which was somewhat suitably settled in the end by a Klizan double fault.
Meanwhile, Svetlana Kuznetsova reached the last four of the WTA Finals for the first time in her career, once again winning her match the hard way.
The 31-year-old Russian only confirmed her place in Singapore at the weekend with a Kremlin Cup triumph, and on Monday she defeated defending champion Agnieszka Radwanska in three sets.
She once more succeeded in three sets yesterday, taking her tally to 22-8 in 2016 matches of that length, to beat Karolina Pliskova and a win for Radwanska later in the day put Kuznetsova into the semi-finals.