Play was stopped during the opening set of the American's 6-7(2) 6-3 6-4 victory when protesters threw large tennis balls with flames printed on them onto the court.

Some of them unfurled banners in the stands calling on tournament sponsors Mubadala and Citi to stop funding the fossil fuel industry.

"I get they're protesting, but there's just got to be a better way to do it," Fritz told reporters.

"I don't understand how people are going to get behind a cause when you're ruining everyone else's good time. Like, it doesn't really make sense to me."

Climate change protesters similarly interrupted play at Wimbledon last month, releasing orange ticker-tape mixed with jigsaw puzzle pieces during two matches.

The second Ashes cricket test at Lord's, the Premiership Rugby final, the World Snooker Championship, golf's British Open and the Grand National horse race have also witnessed climate protests this year.

"It's annoying, obviously, when they do it. It's ruining everyone's time. Everyone wants to watch the tennis. I jokingly said, 'Honestly, this makes me want to go fly on jets more'," Fritz said with a smile.

"I think they're supporting a good cause, but the way they're doing it... Who's going to want to listen when they're just annoying everybody?"

Fritz returned in the evening to seal a 6-3 6-3 victory over Jordan Thompson to storm into the semi-finals, where he takes on Tallon Griekspoor.