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 number one 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.
