The Russian is aiming to add to his 13 weeks at the top of the ATP ratings

Daniil Medvedev needs one more victory to ensure he enters his US Open title defense later this month as world number one, after the Russian overcame Dutch rival Botic van de Zandschulp in their second-round meeting at the Cincinnati Masters on Tuesday.

Medvedev emerged from a tricky test to win 6-4, 7-5 at the hard court showpiece, also known as the Western and Southern Open.

The second set in particular was a challenge for Medvedev, who described it as "not that clean" as he was forced to save a set point on his serve before seeing out the match.

"The first match is tricky and I'm happy that I managed to go though, and hopefully I will raise my level in the next matches," said Medvedev, who was handed a bye in the first round of action.

The Russian, 26, knows that a run to the quarterfinals in Cincinnati will ensure that he heads into the US Open at the end of August with his world number one rating intact.

Medvedev is currently enjoying a 13th week in total at the top of the ATP charts - a record period for any Russian male tennis professional. 

Should he fall at the next hurdle in Ohio, however, the door will be open for current world number three Rafael Nadal to leapfrog him if the Spanish 22-time Grand Slam champion goes all the way to win the title.

Having skipped the Canadian Open with lingering injury concerns, Nadal starts his Cincinnati campaign against Croatia's Borna Coric on Wednesday.

Medvedev next faces the winner of the meeting between Canada's Denis Shapovalov and America's Tommy Paul, with a potential quarterfinal clash with Nick Kyrgios looming.

The in-form Kyrgios defeated Medvedev in three sets last week in Canada, after the Russian had returned to action with a title win at the Los Cabos Open in Mexico.

The Montreal meeting with Kyrgios was followed by an ugly incident as Medvedev confronted an abusive fan, although there were more savory scenes in Cincinnati as Medvedev won praise for signing autographs all the way around the court following his victory, despite the clock already ticking towards 10.30 pm local time.