Germany's Tommy Haas defeated second seed Roger Federer 7-6 (7/5), 6-4 to win the Halle grasscourt tournament on Sunday to become the ATP's second oldest champion.
Playing in front of his home fans, the 34-year-old wildcard added to his triumph at the same venue three years ago to take his 13th ATP title.
Swiss great Federer, the second seed, was seeking a sixth win at this Wimbledon warm-up event having booked his seventh final ticket with a straight sets semi-final win over unseeded Russian Mikhail Youzhny.
Haas, a former world number two, secured his place in the climax with a defeat of compatriot Philipp Kohlschreiber.
After claiming the title Haas said: "This has been one of the best weeks of my career, but I reckon I won't really appreciate what's happened until this evening.
"If someone had said to me beforehand that I was going to beat Roger Federer, probably the best player of all time, I would have thought they were mad.
"It's a special moment knowing that four months ago I didn't know if I would be able to play at this level again. It's a life lesson," said the injury-plagued Haas, who only recently returned to the tour after a 14-month absence.
In that time, he underwent hip and right shoulder surgery which sent his ranking plummeting to 200.
He came into Halle at 87 in the world with Sunday's victory expected to move him back into the world top 50.
France's Fabrice Santoro remains the oldest champion, winning the 2008 Newport tournament when he was 35.
"This would normally be the perfect time to retire, but I am not ready. I hope to play on for a long time," added the German, who went through qualifying at the French Open last month before going onto to reach the third round.
He has also been awarded a wildcard into Wimbledon.
Federer was magnanimous in defeat, saying: "Tommy has performed well throughout, I'm thrilled for him."
Federer, the record 16-time Grand Slam title winner, said he will head to Wimbledon "probably on Thursday".
"It would be great to win there for a seventh time," he said.
Sunday's victory was Haas's third career win over Federer after beating his better-fancied rival at Halle in the semi-finals in 2005 and 2006, against 10 defeats, the last in the semi-finals at Wimbledon in 2009.
Federer broke to lead 3-1 in the opening set but proceeded to lose three successive games to find himself trailing 4-3.
Haas went on to clinch the set on a winning serve in 50 minutes.
In the second set, Haas broke to lead 5-4 and serve for the match, winning when Federer put a return long.