Jack Sock has grabbed a place in the semi-finals of the Swiss Indoors tournament with a 5-7 6-4 6-2 victory over fellow American Donald Young.
The 23-year-old broke serve at the first time of asking, but dropped serve three games later as Donald levelled the set at 2-2.
The pair had a further five break points between them, but none were converted until Young took the set 7-5.
Sock bounced back in the second set with a double break, but Young responded with two breaks of his own.
The set eventually swung in Sock's favour as he snatched his opponent's serve to take a 6-4 lead before holding for the set.
The deciding set was more straightforward for Sock as he needed two breaks of serve to wrap up the match as Young could only get two games on the board.
