STUTTGART, Germany - After nearly three months out of action, Roger Federer said he was not shocked by his loss to 39-year-old Tommy Haas at the Stuttgart grasscourt tournament on Wednesday.

Haas, a former world No 2 but now No 302, won 2-6, 7-6 (8), 6-4 for just his fourth victory in 17 meetings against his close friend.

Federer, building up for an assault on an eighth Wimbledon title, hadn't played since March, skipping the entire claycourt season.

It was just the second loss of 2017 for the 35-year-old, who claimed the Australian Open for his 18th major in January.

"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."

The victory advances Haas in his first quarterfinal since Rome in 2014.

Despite a superb first set, the 35-year-old Federer squandered a match point and lost his grip on the game in the oldest tour match, in terms of combined ages, since 1982 and suffered only his second loss of the season.

"I thought it was a typical grasscourt match today. The rallies weren't very long and it was decided on a serve there or a return here," Federer said at his post-match media conference.

"If you don't take your chances like I didn't, leading a set and a break, you really only have yourself to blame at the end. You have to acknowledge the fact that he was a bit better. It's quite frustrating, but that's the way it goes sometimes."

"I definitely was not as sharp as I was hoping to be in maybe the big moments, or the moment when I had the lead and where I feel I should have been cruising from that moment on."

Federer also held match point in his only other loss this year, to Russia's Evgeny Donskoy in Dubai.

"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.

"I saved a match point in the second set and after that I was able to play more freely. I even shocked myself with the way I was hitting the ball."

Haas is the oldest player to beat a top five opponent since Jimmy Connors, at 39 years and five months, defeated Michael Stich in Memphis in 1992.

He is also the lowest-ranked player to beat Federer since No 407 Bjorn Phau at Washington in 1999.

"I am speechless, of course," Haas said. "There are a lot of emotions when you are playing a close friend.

"When you come into the second set, save a match point and then come back, that always makes you very happy about a win. I am shocked with how I was able to do that."

Federer, who fired 23 aces, had match point at 8-7 in the second set tie-breaker but drilled 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 (1), 6-2 in 83 minutes.

AFP - Reuters