Roger Federer will make a delayed start to the hardcourt season as the main draw of the Cincinnati Masters gets under way Monday with Serena Williams poised to return in the ATP-WTA event.
The last major tune-up prior to the August 28 start of the US Open gives men and women a final chance to polish their form before the final major of the season.
Former world number one Williams will be back on court a fortnight after the worst loss of her career, with the 23-time grand Slam champion playing unseeded, opening against Australian Daria Gavrilova.
The Wimbledon finalist continues to try and balance motherhood with a return to tennis almost a year after giving birth to her daughter.
Federer opted out of the Toronto stop on the ATP, preferring to concentrate his pre-Open energies on lifting an eighth Cincinnati title after taking the honours at four of the last six editions.
The event played at a venue on a motorway exit deep in the American flatlands will also serve as the re-entry point for Britain Andy Murray.
The Scot broke down in tears during a late-night, three-hour battle at the Washington ATP event but was unable to muster the strength to return the same day for a quarter-final.
Murray has been making a cautious return after his January hip surgery and refuses to push his luck.
"I need to be careful and to listen to my body as I come back from a long-term injury," the 31-year-old said after withdrawing in the US capital.
The number 375 will begin against French 16th seed Lucas Pouille, Murray's eighth match since returning in June.
Federer, top seed Rafael Nadal and the rest of the men's top eight have byes into the second round.
Federer follows Nadal, with Toronto quarter-finalist Alexander Zverev on third ahead of Juan Martin del Potro, forced to pull out in Canada with a wrist problem.
Nadal, who come back from injury again this season, is pleased with how he is holding up on the cement which he has never favoured.
"I know I am playing well since I came back from the injury. I need to play well now on hard again - so let's make that happen," the US Open holder said.
Women's number one Simona Halep, who lost the 2017 Cincinnati final to Garbine Muguruza takes the top seeding, ahead of Australian Open winner Caroline Wozniacki.
Muguruza is seeded seventh after failing to start matches in both California and Montreal due to injury. She comes onto the cement cold and will wait for an opponent in the second round.
US Open winner Sloane Stephens is seeded third, followed by Wimbledon champion Angelique Kerber, a first-round loser in Canada.
Stephens made it to the weekend in Canada as her form falls into place.
"When you're playing good matches in big tournaments, I don't think it's peaking too soon," she said. "It's just getting confidence and playing good tennis."
Switzerland's Roger Federer, pictured July 2018, will start late at Cincinnati Masters event as Serena Williams is poised to return