Andy Murray was knocked out of the Rafa Nadal Open on Thursday as Matteo Viola won the biggest match of his career in three sets.
Murray, who was continuing his comeback from hip surgery, had dispatched teenager Imran Sibille and Norbert Gombos at the ATP Challenger Tour event.
But the Scot, currently ranked 329th in the world, lost 3-6 6-4 7-6 (7-3) to 32-year-old Viola, who broke Murray five times to seal a famous win.
"I'm cramping. Very tired," said Murray after his defeat by world No 240 Viola. "I would have liked to have played more matches but it was good. I played two competitive matches. Physically I need to get better."
The former world No 1 competing on the circuit for the first time since 2005 started strongly by winning the opening set, but Viola, who reached a career-high 118 in 2018, held his nerve to send the match into a deciding set.
Murray appeared to struggle on serve and took a couple of injury timeouts as the match headed into a tie-break. The three-time major winner had a look of frustration on his face which was summed up when he double-faulted on match point.
Viola will next face Blaz Kavcic, a Slovenian ranked 239th in the world.
Murray returned to the courts in June playing doubles, including Wimbledon, before pulling out of the doubles at the US Open to concentrate on his singles career.
He had lost in the first round of Cincinnati and Winston-Salem before taking the decision to compete on the second-tier Challenger Tour for the first time since 2005.