Roger Federer and Novak Djokovic are without a doubt two of the greatest players ever to grace a tennis court. With 169 singles titles between them, and a combined total of 34 career Grand Slams, both are sure to go down in history.
Almost as famous as their legendary ability, however, is their intense rivalry that has entertained tennis fans from all over the world over the past decade.
The pair have faced off a total of 46 times - with Djokovic leading by 24 wins to Federer's 22 - both men are all too familiar with each other's games and styles.
But thanks to the beauty of the Laver Cup, they actually found themselves on the same side of the court on Friday in Chicago.
Federer and Djokovic teamed up to take on Kevin Anderson and Jack Sock on day one of the annual battle between Team Europe and Team World.
Despite the fact that the two greats had teamed up this time around, it appeared that some habits are harder to break than others.
After Djokovic had served to Sock in the third game, the return came back to the towering Serb who immediately aimed a powerful return back across court.
Only it didn't make it over the net and instead fired straight into the back of his partner Roger Federer.
The current Wimbledon and US Open champion was quick to see the funny side, however, and immediately rushed to Federer's aid before giving him a hearty rub on the back to make amends.
Federer too seemed to appreciate the comedic aspect of the moment, sharing a wry smile and a laugh with Djokovic before shaking hands and continuing with the game.
In spite of their bitter on-court rivalry, both men are said to share a growing friendship outside of the sport, with both previously having spoken extremely highly of the other.
But amazingly their combined powers were not enough to triumph, with the pair eventually going on to lose the match up 7-6, 3-6, 6-10, to Sock and Anderson.
Team Europe fared slightly better overall for the whole day, winning all of the opening singles' matches and ending day one with a 3-1 lead over Team World.