Jack Sock joins Federer in ATP World Tour semis
By Hu Shichen
["china"]
World number two Roger Federer maintained his unbeaten run at The ATP World Tour Finals in London with a come-from-behind victory over Milan Cilic.
Federer had already secured his place in the semi-finals before his final round-robin match on Thursday in which he claimed a  6-7 (5-7), 6-4, 6-1 victory.
The Swiss maintained his impressive record of only having lost four times all season. 
He also stayed on track for the potential maximum award of 1,500 rankings points if he wins all five matches at the tournament. This would send him into 2018 right on Rafael Nadal’s tail, only 140 points behind. 
Jack Sock in action /VCG Photo

Jack Sock in action /VCG Photo

The second match of the day was essentially a quarter-final between American Jack Sock of the United States and Germany's Alexander Zverev, who both had a chance to get to the semifinals for the first time in their careers.
Sock eventually come through 6-4, 1-6, 6-4 in an entertaining encounter and will meet Grigor Dimitrov in one semi-final.
Federer's next opponent will the winner of Friday's match between Dominic Thiem and David Goffin. 
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