After winning the campaign opener against Jack Sock, Roger Federer continued his winning momentum as he registered a three-set win against Alexander Zverev to reach the semi-final of the ATP World Tour Finals. In another clash, Sock claimed his first win by beating Marin Cilic 5-7, 6-2, 7-6(4).
Zverev entered the round after winning a tough encounter against Cilic in the last round. Right from the start of the match, he showed the intensity that could have put Federer under pressure winning the first three points of the match on the Swiss maestro's serve to secure three break points. However, Federer fought back and ended up winning the game. Both the players stayed toe-to-toe and with no one able to gain an advantage, the set had to be decided via a tie-breaker. It was Federer who secured the set but not before Zverev had saved two set points. successfully denied two set points before the tie-break.
The German looked rattled early on in the second set as the Swiss broke him in the very first game and it looked like the match might have a quick end. However, Zverev fought back and with the help of some Federer weak service games from Federer clawed his way back into the set
In another clash, Marin Cilic clashed with Jack Sock in a do-or-die game, after both had lost their openers against Zverev and Federer respectively. The game started with both the players showing immense persistence and competitiveness, breaking each other in the first two games of the match. However, it was Cilic, who broke the American in the 12th game of the first set to take a slender lead in the match. However, the American was not quite ready to lie down and after breaking Cilic in the first game, he kept the latter at arm's length my holding his serve in a 15 point game. Sock eventually won the second set 6-2 and set up a decider under the lights at the O2 Arena.
But all the momentum that Sock had built in the second game seeped away in the second as Cilic broke early to take a 2-0 lead. However, Sock, yet again, dug deep and broke back to bring the score to 3-2. The match eventually came down to a tie-breaker where Sock held his nerve and sealed his first win in the competition.