NEW YORK — Roger Federer gave away a lead against a guy he’d never lost to and was beaten 3-6, 6-4, 3-6, 6-4, 6-2 by 78th-ranked Grigor Dimitrov in the US Open quarterfinals before a stunned crowd at Arthur Ashe Stadium.
The 38-year-old Federer took a rare-for-him medical timeout after the fourth set, leaving the court with a trainer. It was not immediately clear what might have been wrong with Federer, although he did appear to be flexing his back after some points.
When play resumed after a break of nearly 10 minutes, Federer’s form never picked up. He finished with 61 unforced errors, 33 on the forehand side.
The third-seeded Federer had been 7-0 against Dimitrov, taking 16 of their previous 18 sets.
Federer is now 43-2 in his US Open career against players ranked outside the ATP’s Top 50. His other loss came last year in the Round of 16, against the 55th-ranked John Millman.
Federer would have been the oldest Grand Slam semifinalist since Jimmy Connors was 39 at Flushing Meadows in 1991. He also was trying to add to his totals of five US Open championships and 20 major trophies in all.
Instead, Dimitrov advanced to his third major semifinal, first in New York. He will face No. 5 Daniil Medvedev on Friday.
The Associated Press contributed to this report.