There was a brief delay in the start of the second set of the tennis match at the O2 Arena after a protester set his arm on fire.
The activist, carrying a lighter and wearing a white T-shirt with a message about private jets, went to the black court and sat down near the net. Security guards carried the person away.
The thing came out of the blue. The runner-up at the French Open said he had never had an incident like this on the court. I hope he is doing well.
He spoke to the chair umpire to make sure it was safe to play and to ask that a mark on the court be cleaned up.
The man was quickly removed by security after he accessed the court. The situation is being handled by the police after play was halted.
Team World's Schwartzman was defeated by Team Europe's Tsitsipas in a match that gave Team Europe a 2-0 lead.
The 20-time Grand Slam champion was scheduled to compete hours later Friday in his final competitive match, teaming up for doubles with his long-time rival.
After a series of operations on his right knee, Roger Federer has decided to end his playing career.
There have been other instances of high-profile tennis matches being interrupted in recent years, including during the 2009, when a man tried to put a hat on the Swiss player.
At this year's French Open, in June, a protester wearing a T-shirt with the message, "We have 1028 days left," interrupted the men's semifinal between the two players.
The AP contributed.