World number one Jannik Sinner had to go the full distance before outlasting Jan-Lennard Struff 6-2, 6-7 (1-7), 7-6 (7-3) on Friday for a place in the semi-finals of the Halle grass court tournament. Sinner failed to convert all of his 11 break points in the second and third set against Struff, who fired 18 aces, before eventually prevailing in the final tie-break after 2 hours 30 minutes. “It was a very tough match. I had chances in the second, had chances in the third, but couldn’t use them. It was 0/40 [in the first game of the third set]. I just try to accept these kind of challenges,” Sin…