Roger Federer was upset by Tommy Haas in the second round of the Mercedes Cup in Germany on Wednesday.
The battle of the veterans saw Haas save a match point and go onto edge the 18-time grand slam winner 2-6, 7-6(8), 6-4 on the grass courts of Stuttgart.
The result marks Federer's second loss of the season in 20 matches.
After blitzing the opening set in just 22 minutes, it looked like Federer was on track for a routine win.
But the turning point would come when the 39-year-old Haas saved match point deep in the second set tiebreaker and went on to force a third set.
The German then went on to save no less than seven break points in the final set while earning a break of serve that would see him advance to the quarter-finals.
Waiting for Haas in the last eight is Mischa Zverev, who defeated Yannick Hanfmann 7-6(1), 6-2 earlier in the day.
Elsewhere, fifth seed Steve Johnson was knocked out by Philipp Kohlschreiber, losing 6-7(3), 7-5, 6-7(6).
— MercedesCup (@MercedesCup) June 14, 2017