Andy Murray's last-16 defeat to top seed Taylor Fritz was interrupted by climate protesters at the Citi Open in Washington DC.
Play was halted for five minutes in the first set as three giant tennis balls were thrown on to the court.
The protesters were then escorted from the stands before play resumed.
Murray, 36, came from a break down to take the first set on a tie-break but Fritz fought back to win 6-7 (2-7) 6-3 6-4.
Murray was playing in his first tournament since his second-round loss to Stefanos Tsitsipas at Wimbledon.
American world number nine Fritz entered the tournament in good form after winning the Atlanta Open last week for his sixth ATP career title.