Kevin Anderson beat John Isner to a place in the Wimbledon men's final following a titanic struggle spanning six hours and 35 minutes of gruelling tennis on Friday.

The match was the second-longest in the tennis championship's history and the longest ever semi-final.

While the pair battled it out on court, fellow semi-finalists Rafael Nadal and Novak Djokovic waited in the wings.

And on social media, everyone made the same joke.

The Times' tennis correspondent Stuart Fraser was among those to note the match's unusually long duration. But he was far from the only one.

"This umpire in the Isner Anderson game had black hair when it started," comedian Jack Whitehall remarked of the silver-haired official.

Former Pakistan cricketer Bazid Khan worried what would become of the players after such an exhaustingly long game.

The US Open's official Twitter account feared for the Wimbledon spectators.

Some social media users were more concerned about how Nadal and Djokovic were passing the time in the locker rooms, patiently waiting for their turn to play.

While some suggested they were sleeping their way through the game, others worried the delay could markedly alter the standard of their forthcoming clash.

One fan worried that time was running out altogether.

They needn't have worried. Djokovic took to Instagram to explain how he was passing the time. Marbles, apparently - though there is no word on whether the long wait caused him to lose any.

Image copyright Novak Djokovic/Instagram

It is not the first time John Isner has been involved in a Wimbledon epic. In 2010, the American's victory over French qualifier Nicolas Mahut took more than 11 hours. He eventually won the final set 70 games to 68.

South African Kevin Anderson will face either Rafael Nadal or Novak Djokovic in the final on Sunday.