Andy Murray beat fourth seed Alexander Zverev 7-6 (7/5), 2-6, 7-5 in a marathon that lasted more than three hours on Wednesday to reach the quarter-finals of the Qatar Open. 

Germany's Zverev served for the first set at 5-4, but Murray dug deep to force the tie-break before winning the opener 7-6.

Poor serving saw the three-time Grand Slam champion lose the second 2-6, but 35-year-old Murray won the epic thriller after he was twice two points from defeat on his serve in the third set.

In his on-court interview after the victory, Murray said the crowd helped him.

"It makes a big difference for the players when we come and get a lot of energy and a great atmosphere from the crowd," Murray said.

The British former World No. 1, will face French qualifier Alexandre Muller, who upset Dutch eighth seed Botic van de Zandschulp 6-2, 6-4.

Murray and Muller have never met. 

"Not so familiar," said Murray. "My coach will obviously watch video and stuff tonight to get a bit more familiar with his game, but it's an opportunity for me in the quarters tomorrow."

Top-seeded Andrey Rublev, the Doha winner in 2020, was in danger of suffering a fourth opening-match exit in five tournaments this year before fighting his way back from 2-5 in the third set to edge Dutchman Tallon Griekspoor 1-6, 6-1, 7-6 (8/6).

Rublev will face Jiri Lehecka, a 21-year-old Czech, who beat Finn Emil Ruusuvuori, 6-2, 7-6 (7-2). 

Canadian second seed Felix Auger-Aliassime struggled against Jason Kubler's serve in the first set but recovered to overcome the Australian 4-6, 6-1, 6-4 after two hours and 16 minutes. 

Kubler had won the only previous meeting, in Newport last year. 

(With input from agencies)