One of the biggest wins of Alexander Zverev's career was tainted by a ball boy interrupting a point during a crucial second-set tiebreaker.
Zverev denied Roger Federer a shot at a 100th career title with a 7-5, 7-6 (5) victory on Saturday to advance to the championship match at the ATP Finals.
Federer was leading the tiebreaker 4-3 and was in the ascendancy of a rally on a Zverev service point when a ball boy at the back of the court dropped a ball. Zverev immediately signaled for the point to be stopped and the umpire ordered the point to be replayed.
Zverev served an ace before going on to close out the match moments later.
"I want to apologize for the situation in the tiebreak," said Zverev, who was booed by some members of the crowd during his on-court interview.
The ball boy dropped the ball so it’s in the rules that we have to replay the point. I’m a little bit upset about the whole situation because this is not how I wanted it to end.Alexander Zverev
Zverev, 21, is the youngest player to reach the final of the season-ending event since 2009 and the first from Germany since 1996.
Federer, 37, was seeking a record-extending seventh title, but was unable to cope with the pressure created by Zverev's power and precision at the O2 Arena.
An inspired series of shots earned Zverev the first break points of the match in the 12th game and Federer sent a forehand wide to fall behind.
Federer broke for a 2-1 lead in the second set, but Zverev quickly composed himself to hit straight back in the following game.
Zverev then played a nerveless tiebreaker, despite the freak interruption, to set up a title decider with either Novak Djokovic or Kevin Anderson, who will play in the other semi-final later on Saturday.
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