Nick Kyrgios pulled off a stunning upset, upstaging top seed and incoming world number one Rafael Nadal 6-2 7-5 to reach the ATP Western and Southern Open semi-finals.

Both players were forced to play back-to-back matches in Cincinnati on Friday after rain wreaked havoc on Thursday.

Kyrgios returned to complete a last-16 win over Ivo Karlovic, while Nadal – set to return to the ATP summit on Monday – outclassed Albert Ramos Vinolas in their rearranged fourth-round tie.

But Nadal was below his best against the maligned Australian and four-time ATP Tour winner, who will face David Ferrer in the final four, having never progressed beyond the second round in Cincinnati previously.

Nadal and the Cincinnati crowd were stunned from the outset as Kyrgios steamrolled the 15-time grand slam champion with some jaw-dropping tennis.

Kyrgios – locked in with his hard and deep groundstrokes – broke Nadal in the opening game after the latter sent a forehand long.

It was not until the third game that Nadal hit a winner but it meant nothing as Kyrgios claimed the double-break for a 4-0 lead inside 12 minutes after chasing down the Spaniard's attempted drop shot.

Nadal – who tallied 10 unforced errors and won just 11 of his 20 first service points in the opening set – continued to be uncharacteristically sloppy and while he eventually got on the board, he was helpless to stop a Kyrgios onslaught.

There were signs of life from Nadal early in the second set but he was soon on the backfoot as Kyrgios broke serve for a 3-2 lead.

You could hear a pin drop in the stadium when Kyrgios – a two-time ATP 1000 semi-finalist in Miami – consolidated his advantage.

Kyrgios had the chance to close out the match on Nadal's serve but he was thwarted by the veteran, who suffered a last-16 loss at the Rogers Cup last week.

There was a wobble from Kyrgios, double-faulting twice when serving for a spot in the semis as Nadal put the match back on serve in the 10th game, but it was only a wobble as the Aussie posted his 100th ATP victory.