Alexander Zverev reached the final of the ATP Finals in London on Saturday with an impressive straight sets win over Roger Federer, although the German's victory was somewhat overshadowed by an unusual incident at a key moment.
Zverev, 21, defeated world No 3 Federer 7-5, 7-6 to move within one win of the biggest title of his career while preventing the Swiss great from contesting for his 100th trophy.
However, boos rang out around the stadium from the pro-Federer support at the end of the match in response to Zverev stopping a rally during the second set tie-break. With Federer leading 4-3, a ballkid dropped a ball, forcing the point to be replayed.
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Zverev won the point with an ace and nudged into a 5-4 lead before Federer netted with a simple forehand volley to hand the German two set points, the second of which he took on his own serve.
Immediately after the match finished there were jeers inside London's O2 Arena and on-court interviewer Annabel Croft told them to be "more respectful" as Zverev had been playing by the rules.
"First of all I want to apologise for the situation in the tie-break," said the German. "The ball boy dropped the ball and it is the rules we have to stop the point."
"I'm unbelievably proud," added the world No 5. "My team and me have been working so hard for this.
"I'm a little bit upset now about how it all ended, I didn't want it to end that way, but hopefully I'll have many more great matches here."
Serve dominated the first set of a high-class match, with neither player able to make serious inroads, Zverev sending down serves around the 140 miles-per-hour mark.
Six-time champion Federer, 37, and third seed Zverev both showed a willingness to get to the net in a match featuring power and guile.
The Swiss veteran eventually faltered in the 12th game of the opening set, watching helplessly as Zverev zipped a magnificent passing shot past him down the line on his way to breaking to love.
The second seed regrouped and drew first blood in the second set, breaking in the third game with a thunderous backhand down the line that drew enormous cheers from the partisan crowd.
But the frustrated 20-time grand slam winner could not consolidate his position, losing the next game as Zverev levelled at 2-2.
Federer's level slipped as his young opponent stayed focused but he clung on to take the set to a tie-break.
The tie-break went with serve until the 10th point, when Federer netted to hand Zverev a mini-break - an advantage he did not squander.
Zverev, who already has three Masters series titles under his belt in his short career, is the youngest finalist at the event since Juan Martin del Potro in 2009.
