Frances Tiafoe has recorded one of his best wins this year by beating Italy's Matteo Berrettini in the opening round at the Cincinnati Masters.

World No.25 Tiafoe was a 7-6 (7-3) 4-6 7-6 (7-5) victor over the 12th seed in two hours 52 minutes to set up a second-round clash with fellow American Sebastian Korda, who saw off Russia's Karen Khachanov 6-3 6-4.

"I really just needed this. I know it's a first-round match ... But everyone knew why I needed this against a quality player, so it was big," the 24-year-old said in his on-court interview.

"I know I've beaten a lot of these guys, but it hasn't happened of late. So it's one of those things where you've got to get over the hump. But I'm happy I get another chance to play again."

16th-seeded Bulgarian Grigor Dimitrov was another round-of-64 casualty, beaten 7-6 (7-4) 6-3 by Denis Shapovalov of Canada.

Earlier on Monday, 12th-seeded Argentine Diego Schwartzman found his form late to beat Alex Molcan 5-7 6-4 6-2 while Croatian 13th seed Marin Cilic's resurgent season continued with a routine 6-3 6-3 win over Spanish qualifier Jaume Munar.

Robert Bautista Agut, the 15th seed, enjoyed a 6-7 (5-7) 6-4 6-2 victory over Francisco Cerundolo while Americans John Isner and Marcos Giron also advanced.

Andy Murray pulled off an epic three-set win over fellow tour veteran Stan Wawrinka.

In a 22nd matchup between the multiple grand slam champions trying to put injuries behind them, Murray triumphed 7-6 (7-3) 5-7 7-5 in just under three hours.

Murray, 35, and Wawrinka, 37, both required multiple visits from trainers to treat leg problems during the tournament that serves as a tuneup for the US Open.

"I was hanging on in the third set," Murray said.

"I was struggling a bit. So was Stan. We're not young any more."

Next up for the Scot is an all-British battle with ninth seed Cameron Norrie, who beat Denmark's Holger Rune 7-6 (7-5) 4-6 6-4.

Australians Nick Kyrgios, Alex de Minaur and Thanasi Kokkinakis are all in action for the first time in Ohio on Tuesday (Wednesday AEST).

With Reuters.