Halle: Roger Federer loses in semi-final of Wimbledon warm-up event
Roger Federer suffered a shock defeat by German teenager Alexander Zverev in the semi-final of the Gerry Weber Open in Halle, Germany.
Federer, who was bidding for a ninth Halle singles title and his fourth in a row, lost 7-6 (7-4) 5-7 6-3.
Zverev, 19, claimed the biggest win of his career, becoming the first teenager to beat Federer since 2006.
The Swiss will begin his bid for an eighth Wimbledon singles title later this month.
Federer, 34, had previously won 15 straight sets at Halle but Zverev, standing 6ft 6in and ranked 38th in the world, dropped just four points on serve in the opener and won it 7-4 in a tie-break.
The 17-time Grand Slam winner hit back, claiming the first break of the match at 5-5 and serving out the second set.
But Zverev - born in Hamburg to Russian parents - broke in the sixth game of the decider and held on to win in just over two hours, becoming the first teenager to beat Federer since Andy Murray, then aged 19, in Cincinnati in 2006.
"It's a grass-court match - if you miss the chances you pay the price," said Federer. "It worked well for him. I missed too many chances. At the end he was just a little bit better."
Federer said he had work to do before the start of Wimbledon on 27 June after his second loss on grass this month.
He was also beaten by Dominic Thiem in the semi-finals of the Mercedes Cup in Stuttgart last week.
"There are little things that have to fall into place then I will play better and feel better," added Federer. "I hope that happens sooner rather than later.
"I have to see how I feel at the beginning of Wimbledon. I know the dangers of the early rounds of any Grand Slam.
"I now know what I need to work on in the next 10 days. Clearly I need some rest. It has been intense and busy and that is exactly what I have needed, and at least I have a clear picture if where my game is at and what I need to do."