Kyrgios has positioned himself perfectly for a US Open charge after beating Nadal 6-2 7-5 at the Cincinnati Open a week before the last grand slam of the year.

He will play David Ferrer in the semi-finals on Sunday. Making the win against Nadal more impressive was the fact Kyrgios had to back up from a tough three-setter against big-serving Croatian Ivo Karlovic earlier in the day.

Kyrgios now has a two wins and two losses record against Nadal, who returned to the No. 1 ranking this week for the first time since July 6, 2014.

Kyrgios is the only player to beat 10-time French Open champion Nadal, Roger Federer and Novak Djokovic in their respective first meetings.

But both Spaniard Nadal and Kyrgios has the people of Barcelona on their minds after the match. Nadal wore a black ribbon on his jacket to honour the Barcelona victims.

"Of course everybody is destroyed in Spain, including me," Nadal said.

"[It's] a tragedy, the feeling that you are not safe ... So that's terrible. So just very sad. I'm very, very sorry about what happened to all the victims, all the families, friends.

"[This] is the moment to be together like a country and all being together, we go through these kind of things."

World No. 23 Kyrgios was back to his brilliant best against Nadal, proving he had overcome a hip injury for a timely boost to his US Open bid.

The Canberra junior hadn't beaten Nadal since their spine-tingling clash at Wimbledon in 2014, which announced Kyrgios as a future star.

The 22-year-old has been on a rollercoaster ride since that moment and has won three career titles, but he is yet to breakthrough the quarter-final barrier at grand-slam tournaments.

His best result at the US Open is making the third round. He has been battling a nagging hip injury, which forced him to withdraw from Wimbledon in July.

But his performance against Nadal will fire a warning shot to his rivals before the US Open begins on August 28.

Nadal made Kyrgios scrap in the second set and broke Kyrgios' serve to level at 5-5 as he fought to save the match.

But Kyrgios held his nerve and secured a straight-sets win with a booming ace. It was Kyrgios' 100th ATP win.

"Nick is a great player, but I played bad, obviously," Nadal said.

"He obviously is a tough match always. Nick is a great player, but I played poorly.

"I started the match well and then I played a very bad game in the second set when he broke me. I played some good points.

"He had some mistakes and I was able to be back in the match. And then I played a terrible game. So it was a bad match for me."

The challenge now is making sure he carries the momentum into the US Open as he prepares to rest his body next week.

"Little kid playing on centre court of Cincinnati against Nadal, that's the way, the best has to come out," Kyrgios said.

"The problem for me is trying to bring it on an everyday basis, say, centre court of Lyon with, like, 5 people against Nicolas Kicker earlier this year, I lost.

"Tonight I'm playing Rafa and I win. These matches aren't the problem. It's those matches for me.

"Obviously I think it's easier to say that for me because you see me tank ridiculous amounts of matches against, like, on back courts and stuff like that, and you never see me doing anything silly obviously in a match like this.

"It's easy to get up for these matches."

Kyrgios had little time to recover before clashing against Nadal after bouncing back to beat Karlovic in three sets 4-6 7-6 (8-6) 6-3.

"In the last couple of months I had a rollercoaster of scenes," Kyrgios said.

"Ever since Davis Cup, had such a big high. Obviously my grandpa passed away. Had some off-court issues. My head's been all over the place.

"I have just been going through a load of shit, sorry for cussing, but a load of stuff that's distracted me from just trying to play some tennis, and hopefully I'm just trying to get on the right track again."