World number one Novak Djokovic won another gruelling battle in Doha to continue his unbeaten start to the year and progress to the Qatar Open semi-finals.

The Serb came from a set down, just like in his previous match, to beat Georgia’s Nikoloz Basilashvili 4-6, 6-3, 6-4 in a match lasting almost two hours.

Djokovic will play Spain’s Roberto Bautista Agut in Friday’s semi-final, who beat three-time Grand Slam winner Stan Wawrinka in straight sets 6-4, 6-4.

And, ominously, for his opponents said he still plenty of room for improvement.

“I feel I have a gear or two (to go) up still,” said Djokovic.

“Under the circumstances I managed to find a way to win against a player that is hitting the ball very fast and just being very aggressive and it’s hard to predict where the ball is going to go with a player like him.”

It was the first time Djokovic has won back-to-back matches from a set down since Cincinnati in August last year, a tournament he went on to win.

As on the previous evening, where he struggled against Hungary’s Marton Fucsovics, the Serb started slowly.

He lost his first service game and never recovered the break as Basilashvili, the number five seed, powered by a blistering forehand took the first set.

However, Djokovic’s fortunes changed in the second set when he broke the Georgian in the fifth game and slowly took control of the match.

By contrast, Djokovic’s opponent in the semi-final is yet to drop a set this week.

However, the Serb, twice a previous tournament winner in Doha, remains the overwhelming favourite to win the tournament and now has a 15-1 record overall in Doha.

After securing his semi-final berth, the irrepressible Djokovic then headed back out to court to play his sixth match of the week in the doubles with his brother Marko.

That game he eventually lost, but asked if he was playing too much, Djokovic simply said: “I’m fine, I’ll be fine.”

Also through to the semi-finals is Tomas Berdych of the Czech Republic who brushed aside France’s Pierre-Hugues Herbert, one of the surprises of the tournament, 6-2, 6-4.

Berdych is a former finalist in Doha, losing in 2015 to David Ferrer.

The last semi-final spot went to Italy’s Marco Cecchinato who beat Dusan Lajovic of Serbia 7-6 (7/2), 6-2.