Andy Murray said victory over Tennys Sandgren at the Zhuhai Championships in China was one of his best as he continued his return from hip surgery.
The Scot prevailed 6-3 6-7 (6-8) 6-1 for his first singles victory at Tour level since January.
Murray, who had lost to world number 69 Sandgren in North Carolina last month, will play Australian world number 31 Alex de Minaur in the second round.
"In some ways it's one of the best wins that I've had," said the 32-year-old.
"Not in terms of just getting through that today, but everything that's gone into getting back to this point."
Murray said at the Australian Open that the ongoing problem with his hip could have forced him into retirement.
He instead underwent the resurfacing operation, from which no player has ever returned to play top-level singles tennis.
"It's been difficult and it was undecided at times about whether I wanted to keep going or not and it's been tough," he said.
"I'm really glad that I can actually get the win today and hopefully I'll be able to keep going."
The former world number one's comeback was initially in doubles tournaments, including both men's and mixed at Wimbledon, and he began playing singles competitions at the beginning of August.
Murray, now ranked 413, won two matches on the lower-level Challenger Tour at the Rafa Nadal Open at the end of last month.
This win over American Sandgren is his first on the ATP Tour since beating James Duckworth at the Brisbane International on 1 January.
He missed the opportunity of a match point in the second-set tie-break, only to race through the decider and complete victory in two hours and 41 minutes.
BBC tennis correspondent Russell Fuller
Murray had to work extremely hard for his first singles win on the ATP Tour since New Year's Day.
The fourth game of the final set, for example, lasted 19 minutes and 18 seconds.
But Murray was physically stronger than Sandgren in the decider, and his movement, serve and defense were eye-catchingly good throughout the match.
Given the high levels of humidity in Zhuhai, and the two hour 41 minute duration, Murray will be relieved to have a day to recover before the second round.
Especially as De Minaur, the 20-year-old world number 31 from Australia, is an opponent who will make him work very hard, and run a very long way, for victory on Thursday.