Daniil Medvedev's bid for an elusive first grand-slam title continued to gain momentum as he brushed aside Dominik Koepfer to reach the third round of the US Open.

The second seed, who was a finalist at Flushing Meadows in 2019, following up his first-round thrashing of Richard Gasquet with a 6-4 6-1 6-2 triumph inside two hours.

It was a win far removed from his previous meeting with Koepfer, en route to the final two years ago, when the German won the first set and pushed his opponent to the limit.

But despite handing Koepfer an early break back after breaking in the opening game of the match, the new-look Medvedev was in full control as he surged to a victory that will have his rivals sitting up and taking note.

Medvedev said: "It was a great level from me – there were a few tight moments in the match that I managed to hold well, and I’m really happy to be through in less than two hours."

Medvedev’s compatriot Andrey Rublev, the fifth seed, found the going tougher but still emerged as an ultimately comfortable 7-6 (2) 6-7 (5) 6-1 6-1 winner over Pedro Martinez of Spain.

In a significant upset, world number 117 Botic Van De Zandschulp surged past eighth seed Casper Ruud 3-6 6-4 6-3 6-4 to reach the third round of a grand slam for the first time.

Fifteenth seed Grigor Dimitrov retired with a foot injury as he trailed Australia’s Alexei Popyrin 7-6 (4) 7-6 (4) 4-0.

Elswhere, Stefanos Tsitsipas was jeered by the crowd after taking another lengthy bathroom break during his win over Adrian Mannarino.

The Greek third seed had angered Andy Murray with his long trips to the loo in their marathon five-setter on Monday.

Tsitsipas looked to be cruising into round three when he took a two-set lead against Frenchman Mannarino.

But he was up to his old tricks again after dropping the third set, leaving the court for more than seven minutes.

The late-night crowd on Arthur Ashe made their feelings clear when he finally returned, but the fired-up world number three went on to complete a 6-3 6-4 6-7 (4) 6-0 victory.

Afterwards, Tsitsipas insisted: "I haven't done anything wrong, so I don’t understand. The people love the sport, they come to watch tennis. I have nothing against them. I love the fans.

"But some people don’t understand. They haven’t played tennis at high level to understand how much effort and how much difficult it is to do what we are doing.

"Sometimes we need a short break to do what we have to do."

Clearly irked by criticism from Murray and some other players, Tsitsipas brought up a toilet break the Scot took after the fourth set of his victory in the final against Novak Djokovic in 2012.

When informed that break took less than three minutes, he replied: "OK. So three minutes more makes a difference?"

He concluded: "I’ve done everything the right way. If I haven’t, I should be penalised. I completely agree with that.

"But as far as I know, you know, it is a necessity. It is a need when I’m out there playing, performing."

Another leak, this time in the roof, caused havoc with the scheduling inside the adjacent Louis Armstrong Stadium.

Play between Kevin Anderson and Diego Schwartzman was halted after the torrential rain in New York began blowing in sideways through openings under the roof.

The freak conditions forced the players off the soaking wet court while spectators had to shelter under umbrellas.

The match was initially interrupted for 35 minutes while the surface was dried but after a brief restart – during which 11th seed Schwartzman won the first set on a tie-break – the match was once again suspended.

They resumed following the Tsitsipas match on Ashe with Argentinian Schwartzman winning 7-6 (4) 6-3 6-4.

Angelique Kerber’s clash with Anhelina Kalinina, due on afterwards, had to be pushed back until Thursday.