Former world number one Andy Murray was left frustrated after physically fading on his way to a first-round exit at the Citi Open with a 7-6 (10-8) 4-6 6-1 loss to Mikael Ymer on Tuesday.

The three-time Grand Slam winner failed to convert four set points in the first set before the Swede triumphed in two hours and 50 minutes.

The match was full of momentum swings, with the 35-year-old capitalising on Ymer's own physical issues, appearing to cramp in the second set, to level it up after winning five of the final six games of the set.

But 23-year-old Ymer regained his composure and physical state to race away with the third set for victory, rounding out 37 winners for the match, leaving Murray frustrated.

"It was disappointing obviously," Murray told reporters. "I thought there was some good tennis in the first set. After that, both of us were struggling a bit physically. The level of the tennis was not great.

 "Obviously [I] had chances in the first set to close that out. I had set point at 6-5, then... three in the tie-break and didn't get it.

"I think he seemed like maybe he was cramping a little bit in the second set, but recovered absolutely fine after the break at the end of the [second] set.

"Went off to change and cool off a little bit, and he recovered well for the third, whereas I didn't really. Yeah, just frustrating."

The first-round exit comes after Murray lost in the Hall of Fame Open quarter-finals in Newport to Alexander Bublik when he cramped up in hot and humid conditions.

"Struggled a little bit the past two tournaments with that," he said. "I need to have a little look at that with my team and maybe see why that is, make a few changes."

French veteran Adrian Mannarino took care of Bradley Klahn 6-2 6-4, while Jack Draper beat Stefan Kozlov 7-5 6-2 to set up a second-round date with top seed Andrey Rublev.

World number 112 Benoit Paire also triumphed in the first round on Tuesday, getting past Peter Gojowczyk 7-5 6-4.

Kyle Edmund, Jack Draper, Borna Gojo, Dominik Koepfer, J.J Wolf and Denis Kudla also were victorious, with Alexei Popyrin progressing after a walkover against Wu Tung-lin.