2017 Nitto ATP finals, Day 3 roundup

Roger Federer defeated Alexander Zverev 7-6 (8/6) 5-7 6-1 at the O2 Arena, London, on Monday to reach the last four of the 2017 Nitto ATP Finals.

The World No. 2 will appear in the semi-finals of the season-ending tournament for a record 14th time.

The players entered the match with a 2-2 head-to-head record. Federer had defeated Zverev earlier this year in the Halle Open final and the 20-year-old had German avenged his loss in Canada to win his second Masters title of the year.

The first set was evenly matched and eventually went into a tie-break. Zverev enjoyed a 4-0 lead before Federer bounced back and made it 5-4. At 6-6, the German committed two back to back forced errors, handing the World No. 2 the first set.

Federer broke Zverev in the first game of the second set only for the German to come storming back. The 20-year-old had three break points at 6-5 and Federer could only save two before Zverev unleashed a forehand to claim the second set.

In the deciding set, the German proved to be no match for the Swiss maestro, succumbing 6-1.

In the other men's singles match, Jack Sock defeated Marin Cilic 5-7 6-2 7-6 (7/4) in the Boris Becker group on Monday to stay in contention of reaching the last four.

Sock and Cilic battled it out in a two hours 27 minutes clash, and it was the 25-year-old American who kept his hopes alive at the end.

Sock, who qualified for the World Tour Finals after winning the Paris Masters title earlier this month, was 3-0 down in the final set but came back to level proceedings before stretching the match into a tie-break. Sock was down 4-2 but claimed five consecutive points to knock Cilic out of the tournament.

Meanwhile, in the first men's doubles match on Monday, the Australian-Finnish pair of John Peers and Henri Kontinen edged past the duo of Jean-Julien Rojer and Horia Tecau to win their first match of the tournament.

Peers and Kontinen, who won the tournament last year, defeated the 2015 champions 7-6 (7/3) 7-6 (8/6) in a nail-biting clash.

In the first set tie-break, Peers and Kontinen did incredibly well to construct a healthy 5-1 lead, eventually going on to claim the set.

Tecau and Rojer saved four match points to break the defending champions in the 9th game of the second set to make it 5-4.

The outcome of the set was to be decided in a tie-break and the Australian-Finnish duo led 6-3 before their opponents saved three more match points to stay alive in the game. It was Peers who kept his cool though as he fired a winner at 7-6 to secure the tie.

In the second men's doubles match, the duo of Ryan Harrison and Michael Venus defeated Pierre-Hugues Herbert and Nicolas Mahut 6-7 (7/4) 6-4 10-5 to earn a place in the knockout phase of the Nitto ATP Finals.

With two back-to-back wins, the Kiwi-American pair have already qualified for the semifinals with one more game to play.

Harrison and Venus were broken early in the first set but the World No. 18 pair managed to take the set into a tie-break which they lost 7-4.

The match was dragged in to a super tie-break after Harrison and Venus won the second set 6-4.

It was the Kiwi-American duo that came out on top in the super tie-break to defeat Herbert and Mahut.