American Jack Sock defeated Alexander Zverev to book his place in the last four of the ATP Finals at the expense of the German.

Sock books semis spot

Sock books semis spot

Zverev fought back from 4-1 down in the deciding set, but then lost the last two games as Sock went through to the semi-finals after winning 6-4 1-6 6-4.

The win for Sock, who came into the tournament as the big outsider, clinched second place in the Boris Becker Group and set up a semi-final against Grigor Dimitrov, which will be played on Saturday.

"That was a rollercoaster match," Sock said after the match. "He played well in the second, I didn't have the hottest start in the third, but I kept in there and kept fighting."

Roger Federer was the first player to go through to the last four on Tuesday and the semi-final line-up will be completed by the winner of the Pete Sampras Group match between Dominic Thiem and David Goffin this afternoon.

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