On a day attended by US president Donald Trump, the world No.2 sparked controversy when he appeared to make an offensive gesture in response to heckles from the crowd in New York.
The alleged incident occurred as the Northern Irishman walked between holes during the afternoon fourballs session, but it was a fleeting aberration as the champions opened up a 5.5-2.5 lead over the US.
McIlroy was also millimetres away from putting his side 6-2 ahead with the final putt of an eventful day on the final green.
The day began with Europe producing some scintillating early play to win the morning foursomes 3-1.
After the arrival of Trump between sessions, their momentum was slowed in a tight afternoon of fourballs action, but they still came out with two-and-a-half more points to take a healthy cushion into day two.
McIlroy's apparent indiscretion, which was captured by a TV camera, came after he and Shane Lowry had just won the 11th hole to move two clear against Patrick Cantlay and Sam Burns.
It led to a downturn as they lost the next two holes but a short missed putt by Cantlay on the 14th halted the Americans' charge.
A thrilling match then came down to the final green but McIlroy, after back-to-back birdies on the previous two holes, narrowly missed and the point was halved.
Jon Rahm was in imperious form as he followed up a foursomes win to combine with Sepp Straka for a convincing 3&2 win success over Scottie Scheffler and JJ Spaun.
Tommy Fleetwood and Justin Rose came from behind to see off Ben Griffin and Bryson DeChambeau by one hole. A lengthy birdie putt by Fleetwood on the 16th proved crucial in what was a tense tussle that went the full 18 holes.
It was not all plain sailing for Europe, however, as Ludvig Aberg and rookie Rasmus Hojgaard were swept aside 6&5 by Justin Thomas and New Yorker Cameron Young.
That at least gave the Americans something to cling on to after what was a largely demoralising day in which the early enthusiasm of the home fans, even with Trump on hand, was punctured.
Trump arrived after what had been a fairly one-sided foursomes session.
It was the first time Europe had led after the opening morning's play on US soil since 2004.
Rahm and Tyrrell Hatton led the way as they came from behind to beat DeChambeau and Thomas 4&3. McIlroy and Fleetwood then saw off Collin Morikawa and Harris English in convincing fashion 5&4.
Matt Fitzpatrick and Aberg were similarly impressive as they claimed a shock 5&4 win over world No.1 Scheffler and Russell Henley, but there was no foursomes clean sweep as Robert MacIntyre and Vitkor Hovland lost to Xander Schauffele and Cantlay by two holes.
Scheffler had the worst first day by a top-ranked player since Tiger Woods, losing both of his matches in foursomes.
By himself, Scheffler is winning more often than anyone in golf. But his teams were behind nearly throughout both his matches on Friday.
"We gave ourselves plenty of opportunities," Scheffler said. "It really just came down to me not holing enough putts. We put up a good fight at the end."
with AP
10°C