World number one Jannik Sinner reached the last 16 at the ATP tournament in Halle, Germany after a three-set win over Dutchman Tallon Griekspoor on Tuesday. The 22-year-old Italian had to come from behind to win 6-7 (8-10), 6-3, 6-2 in 2 hours 22 minutes. The Australian Open champion sealed victory on his first match-point and next faces Hungary’s Fabian Marozsan. “It was for sure mentally tough,” Sinner said. “I was 5-1 up in the tie-break in the first set. But this can happen, especially on this surface, it can go very, very fast. I think I was good mentally.” Sinner’s best performance at th…