Aryna Sabalenka detailed her current tennis philosophy on Tuesday, with the three-time Cincinnati Masters semi-finalist revealing she's quick to forget about her losses.

"Every week is a new tournament," the two-time Australian Open champion said as she prepared for a second-round start after a bye at the WTA and ATP Cincinnati Open, the last big test before the August 26 start of the US Open.

"It's good to have a short memory. That helps to keep things moving and working hard and improving."

The third seed reached the semis at the US Midwest venue at the previous two editions as well as in 2018.

She's hoping to soon start improving that record as she comes back from the shoulder injury that forced her to skip Wimbledon.

"Every loss is extra motivation to work hard and improve things -- just to keep going," she said.

"If you're fighting every point and giving all you have in practice and matches you'll have your opportunities. You just have to use them."

Sabalenka said that her tennis also proves to be a welcome contrast to real life. The 25-year-old has been through the wringer over the years, losing her father as well as a former boyfriend who fell to his death from a Miami high-rise this year.

Meanwhile, the WTA number three is determined to improve her Cincinnati record.

"I'm trying to figure out what I need to do to get to the finals. But I don't want to focus on that," she said.

"I want to take things step by step  and try to bring my best tennis every time I'm on the court. If I do that, then I will be able to get that semi-final win."

Top-eight seeds waited for opening opponents to emerge from first-round matches that filled courts Tuesday.

Ninth-seeded Daria Kastkina opened with a 6-4, 6-2 victory over Ekaterina Alexandrova, sending over six aces and breaking four times. The win came as a relief after first-round losses in Washington and last week in Toronto.

Number 15 Marta Kostyuk earned a 6-4, 2-6, 6-4 trip to the second round over Belgian Elise Mertens after nearly two and a half hours and a dozen double-faults.

"I don't know how I won today," the Ukrainian said. "A lot of things did not go my way."

Karolina Pliskova, tournament winner eight years ago, began her WTA campaign 7-6 (7/2), 7-6 (7/3) over Bulgarian Viktorija Tomova while France's Varvara Gracheva put out Australian Ajla Tomljanovic 6-3, 2-6, 7-6 (7/5).

Wimbledon quarter-finalist Lulu Sun, who had to qualify into the field, reached the second round over Czech Linda Noskova 6-4, 7-6 (7/4).

Shelton beats Opelka

In men's play, 12th seed Ben Shelton won a self-described "bot v bot" battle of serving as he held off returning Reilly Opelka 7-6 (7/3), 7-6 (7/3).

The towering Opelka, who missed two years with injury and is only now getting back to the tour, bombed 19 aces in his losing effort against his American compatriot.

Shelton said he trained as best he could for the match by facing big serves from his former ATP player father Bryan.

"It's hard to replicate the angle of Reilly's serve and how high it bounces," Shelton said.

"I've never seen a ball (from Opelka) come at me like that. Some of the serves he hits defy physics.

"But it's good to see him coming back, even if he's not at 100% yet.

"I'm pleased with how I was able to finish."

Shelton booked the second round on the second of four match points with a leaping return winner.

He ended with 20 winners while his opponent hit 31 in the 97-minute contest.

American Alex Michelsen advanced over Dutchman Tallon Griekspoor 6-1, 5-7, 6-2.

China's Zhang Zhizhen beat Giovanni Mpetishi Perricard of France 6-3, 7-6 (7/4). Frances Tiafoe earned a home-soil win, beating Spain's Alejandro Davidovich Fokina 6-3, 7-6 (8/6).