World No. 5 Casper Ruud was defeated by Alejandro Davidovich Fogina at the Canadian Open in Toronto.
Davydovich Foghina defeated the Norwegian 7-6(4) 4-6 7-6(4) before Alexander Zverev dropped just three games to take him down.
But it was a close contest against third-seeded Rudd as the 24-year-old came out on top in a hard-fought, rain-interrupted, three-hour encounter.
„I was very focused on every point,” Davydovich Fogina said after the match. „He had serve to end the match, but I focused on every point and didn’t give up.
„It was very tough. We played long rallies with a lot of pressure. When I broke 4-5, finishing the match showed strength.
Davydovich Fogina took the first set, but he was unable to capitalize on the momentum he had gained as rain halted play for an hour and a half.
The delay worked in Ruud’s favor as he came out firing in the second set and secured the third when he found himself two points from victory.
But a determined Davydovich Fogina roared back to seal a thrilling victory, helped by his 58 winners in the match.
Mackenzie MacDonald, Davydovich Fogina’s quarter-final opponent, advanced to the last eight after beating Canada’s Milos Raonic 6-3 6-3.
Casper Rudd’s defeat in Toronto means Holger Rooney will become the new world No. 5 – a career high.
Elsewhere, second seed Daniil Medvedev maintained his impressive Toronto record with a 6-4 6-4 win over Lorenzo Musetti.
The 27-year-old is chasing his third Masters 1000 crown of the season – having previously won in Miami and Rome – and is now tied with Carlos Algaras for the most wins this time around.
Medvedev will play Alex de Minaur in the next round after the Australian beat eighth seed Taylor Fritz.
Amazingly, the 24-year-old came from 5-1 down in the opening set before winning 7-6(7) 4-6 6-1.
The win meant he was only the fourth Australian since 2000 to have five top 10 wins in a calendar year.