Roger Federer and Tommy Haas
Federer and Haas, good friends off the court, embraced at the end of the three-set thriller. Getty Images

Roger Federer returned to tennis with a bump after being shocked by world number 307 Tommy Haas in his opening grass court match of 2017 at the Mercedes Cup in Stuttgart. The 18-time grand slam champion had not played since April after skipping the clay court season but it was Haas who rolled back the years in the battle of the veterans.

A 2-6 7-6 6-4 victory saw 39-year-old Haas inflict upon Federer defeat in his first grass court match of the season for 15 years. Haas, himself an ex-world number two, is also the lowest ranked player to beat the Swiss since 1999.

Defeat, just Federer's second of the year having lost to Evgeny Donskoy in Dubai, derails his preparations for Wimbledon which starts on 3 July. The seven-time champion at SW19 is among the contenders to take the title having enjoyed a stunning year which started with winning the Australian Open after beating Rafael Nadal in the final.

"I'm a little bit speechless that I beat him today," said Haas, who will retire at the end of the season. "It's been awhile since I have won back-to-back matches and to do it today against Roger is obviously one of my career highlights. It's a very special feeling.

"At the same time he's a very close friend of mine so it doesn't feel like such a celebration in that sense. This is my last phase, so the emotions are different from what they would have been a few years ago. This is sport.

"Unfortunately, one person has to lose and lately a lot of the time it has been me. I was happy to be out there in front of a German crowd playing against a friend, an idol, a legend, the greatest ever. It's fantastic."

After an early exit in Stuttgart, Federer will play at the Gerry Webber Open in Halle which begins on 19 June, where he has won on eight occasion; a tournament which is his traditional warm-up event for Wimbledon.

Federer enjoyed a fine start to the year, winning in Melbourne before taking the times at the Miami Masters and Indian Wells. In his self-enforced absence from the clay court season, Nadal has dominated men's tennis rising to world number two with wins in Madrid, Barcelona and Monte-Carlo before claiming his 10th French Open title at Roland Garros.