World number one Aryna Sabalenka needed just 54 minutes to reach the Cincinnati Open fourth round - but Daniil Medvedev could not hide his frustration after missing three match points in a surprise defeat.

Sabalenka did not face a break point in a 6-1 6-3 win over China's Wang Xinyu.

The Belarusian lost only six points in eight service games and committed just five unforced errors to 17 winners in a composed performance.

It was Sabalenka's easiest win for some time following her fourth-round Wimbledon exit and an early loss in Canada last week.

"To get this win in under an hour [is] an insane result and I'm so happy to be through," the 28-year-old said.

"I think I really trusted myself and I was going for my shots without overthinking.

"That was the weapon of tonight's match."

Sabalenka is the two-time defending champion at the US Open, which begins on Sunday, 30 August.

No woman since Serena Williams in 2014 has won the New York title three times in a row.

Sabalenka's position as world number one is also under threat from Australian Open champion Elena Rybakina.

Four-time major singles champion Sabalenka had a 354-point gap over Rybakina going into Cincinnati.

Rybakina must reach the final to have a chance at surpassing Sabalenka. If Sabalenka reaches the quarter-finals, Rybakina would need to win the title to become world number one.

Sabalenka will face Czech Sara Bejlek for a place in the last eight.

Earlier, fourth seed Medvedev lost his cool after squandering a match-winning position against Brandon Nakashima.

The Russian had fought back from 5-2 down in the first set to take it on a tie-break and had three match points on the American's serve at 5-4 in the second.

However, Nakashima saved them and won a subsequent tie-break - then ran away with the third set to win 6-7 (3-7) 7-6 (7-4) 6-1.

Medvedev hurled his racquet at the electronic boards at the back of the court - briefly breaking it - after missing the match points.

He also kicked the screen and knocked over several microphones after committing 51 unforced errors in a poor display.

"Down match points, I was just trying to tell myself to keep fighting for every point," Nakashima said.

"I'm super happy with the level in the third." (BBC)