Rory McIlroy swore at raucous Ryder Cup fans on Saturday before extra security was deployed to monitor rowdy galleries during the Europe star's afternoon four-ball match alongside Shane Lowry as tensions reached fever pitch.
In his morning foursome match with Tommy Fleetwood, McIlroy - who on Friday had flipped the middle finger to hecklers - used an obscenity as he told noisy fans to "shut up" as he prepared to play a shot.
Later, McIlroy was forced to pack off a putt by a heckler on the fourth hole in his four-ball match with pal Lowry, a move that drew a chorus of boos and prompted McIlroy to ask a rules official if anything could be done about over-the-top annoyers.
As the abuse from spectators continued, extra security staff appeared to have been brought in to keep a watchful eye over the match at Bethpage Black.
Speaking after his and Fleetwood's morning 3&2 victory over Harris English and Collin Morikawa, McIlroy said while he had been expecting a partisan atmosphere, some of the crowd behaviour had crossed a line.
"I don't mind them having a go at us. That's to be expected. That's what an away Ryder Cup is," McIlroy said Saturday. "Whenever they're still doing it while you are over the ball and trying to hit your shot, that's the tough thing.
"Between shots, say whatever you want to me. That's totally fine. But give us the respect to let us hit shots and give us the same chance that the Americans have."
As Europe stretched its lead over the United States, McIlroy became the focus of most of the remarks and insults from the crowd, from the creative to the mundane.
"You really just have to focus on the task at hand," McIlroy said, adding that mental toughness was a requirement.
Even after making an obscene gesture to the crowd on Friday, McIlroy said after Friday's play that the spite being fired his way was "what we sort of expected."
"It was rowdy and lively," McIlroy said. "They made it difficult for us, but I felt like Shane and I, we handled that really well and dug in. Made some good swings and good putts when we needed to."
McIlroy, who dropped to his knees and cried on the 18th green at Augusta after winning the Masters to complete a career Grand Slam, has fed off the intense atmosphere, saying on the eve of the event he has struggled to find a balance on how much to engage with hostile crowds.
"At times in the Ryder Cup, I've engaged too much with that, too much with the crowd," McIlroy said.
"But then there's times where I haven't engaged enough. So it's really just trying to find the balance of using that energy from the crowd to fuel your performance."