Zhuhai - Andy Murray called it "one of the toughest wins I've had" after grinding out his first singles victory on the ATP Tour since career-saving hip surgery in January.
The former No 1 looked exhausted after his milestone 6-3, 6-7 (6/8), 6-1 win over Tennys Sandgren on Tuesday at the Zhuhai Championships.
A three-time Grand Slam winner but now ranked 413 in the world, the Briton has competed mostly in doubles since his major surgery and recently played singles on the lower-level Challenger Tour.
He faces seventh seed Alex de Minaur of Australia in the second round in southern China after coming through a physically demanding test lasting more than two and a half hours.
The 32-year-old looked all in at the end of his tussle with Sandgren, ranked 69th in the world, slumping in his chair and puffing out his cheeks.
"In some ways it was one of the toughest wins that I've had," he said, having similarly blown out his cheeks as he took his seat in the post-match press conference.
"It's good to see I'm still progressing and making improvements.
"Tonight was a really good match to get through but I'll see how I feel tomorrow," Murray added, calling it his longest match since returning to tennis.
"It was important for me to get my first win on Tour since the operation," he said, admitting that he was tired but his hip felt fine.
"Now it's pretty cool to play and not have pain there," he said.
Murray at least has a day's rest with his next match scheduled for Thursday.
There were glimpses of Murray at his best as he sealed the first set in 41 minutes after the American Sandgren planted a backhand wide.
Murray, now attempting to build up his creaking body for the rigours of elite tennis, gave a subtle fist-pump.
The Briton squandered match point in the second-set tie break as Sandgren forced a deciding set.
But the American folded in the third, seemingly affected by a foot injury which required extensive strapping with him 3-0 down in the decider.
Victory was a small measure of revenge for Murray, who lost to the 28-year-old last month in his second singles tournament since his return.
After Zhuhai, the China Open in Beijing and the Shanghai Masters, Murray will return to Europe to compete in Antwerp, making it a testing next month on the long road to rehabilitation.
Prior to facing Sandgren in Zhuhai, Murray told AFP that it would be "naive" and "silly" to think he will ever return to being the player that surged to No 1 in 2016.
Results from the ATP Zhuhai Championships in China on Tuesday:
Andy Murray (GBR) bt Tennys Sandgren (USA) 6-3, 6-7 (6/8), 6-1
Damir Dzumhur (BIH) bt Marco Cecchinato (ITA) 5-7, 6-4, 6-2
Miomir Kecmanovic (SRB) bt Casper Ruud (NOR) 6-2, retired
Alex De Minaur (AUS x7) bt John Millman (AUS) 6-1, 6-3
Zhang Zhizhen (CHN) bt Dominik Koepfer (GER) 7-5, 6-2
Pablo Andujar (ESP) bt Steve Johnson (USA) 2-6, 6-2, 6-1