Haas and Federer. Photo: Thomas Kienzle/AFP
Roger Federer suffered a shock defeat to 39-year-old Tommy Haas at the Stuttgart grass court tournament on Wednesday in the Swiss great's first match after almost three months out of action.
Haas, a former world number two but now down at 302, won 2-6, 7-6 (10/8), 6-4 for just his fourth victory in 17 meetings against his close friend.
"I'm not so shocked to have lost. I knew I could lose against Tommy," said Federer.
"He was so good at the end and if I am happy for anybody, then it's for Tommy."
With a combined age of 74, it was the oldest match on the tour since 1982 as Haas, on a farewell to the sport in 2017, made his first quarterfinal since Rome in 2014.
"It's always special to play a close friend like Roger on grass, always lots of emotion," said Haas, who has undergone nine surgeries in his career to mend a number of ailments.
"I saved a match point in the second set so was able to play more freely after that. I even shocked myself."
Federer also held match point in his only other defeat this year to Russia's Evgeny Donskoy in Dubai.
Haas is the oldest player to beat a top five opponent since Jimmy Connors, at 39 years and five months old, defeated Michael Stich in Memphis in 1992.
He is also the lowest-ranked player to beat Federer since number 407 Bjorn Phau at Washington in 1999.
Federer, who fired 23 aces in the contest, had match point at 8-7 in the second set tie-breaker but hit a backhand long.
The German took his opportunity and converted his fourth set point when Federer double faulted for the first time in the match.
Haas controlled the decider, breaking for 3-1 before going on to take the victory on a second match point.
He will next face compatriot Mischa Zverev who beat qualifier and fellow German Yannick Hanfmann 7-6 (7/1), 6-2 in 83 minutes.
Philipp Kohlschreiber, the runner-up last year, advanced by beating Steve Johnson of the United States 7-6 (7/3), 5-7, 7-6 (10/8) in two hours and 39 minutes.
The 33-year-old Kohlschreiber, who lost to Austria's Dominic Thiem in the 2016 final, has won five of his seven career titles in Germany.