Day four of Wimbledon handed us the most exciting match of the tournament so far, Nick Kyrgios vs Rafael Nadal.
The two have developed quite a rivalry since first meeting in London five years ago when a fresh-faced, 19-year-old Kyrgios beat the former world number one.
They've since met five more times, with both men winning three matches each.
Nadal most recently crossed paths with his Australian rival back in February at the Mexico Open - a tie that he lost.
Following defeat, the King of Clay accused Kyrgios of lacking respect and suggest that his attitude was holding him back. At the time, the 24-year-old was ranked at 72 in the world.
"He is a player who has enormous talent," Nadal said.
"He could win Grand Slams and fight the top positions of the ranking, but there is a reason why he is where he is."
It was Kyrgios' rather unique underarm serving that incensed Nadal that day - and five months on, he's pulled it out once again - this time, on the biggest stage.
Towards the end of the first set, the Australian was 40-love up and produced his party trick to ace Nadal and win the game.
Check out a clip below.
His first underarm serve went down very well with the Wimbledon crowd, with some rising to their feet to give Kyrgios a standing ovation.
But less than half an hour later, he did it again. This time, it didn't go down well with the crowd and boos could be heard around centre court.
That kind of reaction probably isn't going to deter the 'Tennis Bad Boy' from doing it again though.
The needle between Nadal and Kyrgios was clear to see from the very beginning and the Australian's party trick no doubt contributed to the tension between the pair.