The Swiss star was the fourth seed heading into the tournament, but found himself on the back foot when Isner claimed the opening set on a tie break.

Isner would earn a crucial break of serve in the second set and eventually sealed a 7-6, 6-4 win to reach the quarter-finals.

He will face Croatia’s Marin Cilic, who secured a 6-3, 6-4 win over Belgium’s David Goffin today.

Serbia’s Novak Djokovic also eased through, with the world number two claiming a 6-4, 6-4 victory against Spain’s Roberto Bautista Agut.

A tricky clash with Argentina’s Olympic silver medallist Juan Martin Del Porto awaits, as he defeated Kei Nishikori of Japan 7-6, 6-3.

Italy’s Fabio Fognini was unable to back up his surprise win over world number one Sir Andy Murray of Britain, as the home favourite lost 6-3, 6-3 to Germany’s Alexander Zverev.

Zverev will take on Canada’s Milos Raonic, who won 6-3, 6-2 against the Czech Republic’s Tomas Berdych.

In the women’s draw, fifth seed Johanna Konta suffered defeat against the United States’ Venus Williams.

Konta came from a set down to level the match, but the Briton would ultimately lose 6-1, 3-6, 6-1.

Williams will take on reigning French Open champion Garbiñe Muguruza, with the Spaniard having continued her preparations for her title defence by beating Julia Goerges of Germany 7-5, 6-4.

Second seed Karolina Pliskova claimed a 6-1, 7-5 win against Timea Bacsinszky of Switzerland today.

The Czech star will now meet Ukraine’s Elina Svitolina, who came from a set down to beat Germany’s Mona Barthel 3-6, 6-0, 6-0.

The competition is an ATP World Tour Masters 1000 event, as well as a Premier 5 event on the Women's Tennis Association tour.

It is a key preparation event for the French Open, the clay court Grand Slam, due to begin on May 28 at Roland Garros in Paris.