Roger Federer has been knocked out of the ATP Finals as he fell to a 7-5, 7-6(5) semi-final defeat against
Alexander Zverev.
Zverev showed his intention from the beginning of this tie as he took every opportunity to move into the net.
At times, Federer thought he had the answer by fizzing efforts straight at the German with such ferocity he could only direct them wide.
But the pair were never able to come close to breaking each others serve as the pair looked destined for a first-set tiebreak.
That was until Zverev turned up the heat and earned three break points while 6-5 ahead and Federer crumbled, firing a backhand wide at the crucial moment.
Both players regained their composure with clean service games at the start of the second set but then the match began to open up.
Federer got his first breakthrough of the showdown - but only just - taking the third of three break points with an expertly executed backhand slice.
However, Zverev showed exactly why he is regarded as a future Grand Slam winner as he responded at exactly the right time with a clean break in the next game for 2-2.
The second set headed straight for a tiebreak and it was Federer who buckled first, volleying into the net at 5-5 to allow Zverev to serve for the match.
Zverev was booed after the victory was confirmed by the majority inside the O2 Arena.
The fans were unhappy with Zverev stopping midway through a point during the tense tiebreak because a ball boy dropped a ball on court.
The point was made to be replayed and Zverev held his serve.
But he apologised for the fracas during his on-court interview - which was interrupted by further boos.
"First of all I want to apologise for the situation in the tie-break," says Zverev.
"The ball boy dropped the ball and it is the rules we have to stop the point."
Sky Sports pundit Annabel Croft, who was interviewing Zverev on court, came to his aid.
"I'm not sure why you're all booing. I think you have to be a little bit more respectful he was playing by the rule," she rightfully said.