The US drew first blood at the 36th Ryder Cup but holders Europe forged ahead by 2-1/2 points to 1-1/2 after yesterday's opening fourball encounters at the K Club.
The cup holders won two and halved one of the four ties with the Americans winning one and halving one.
Tiger Woods, who rallied after a woeful display on the front nine, and Jim Furyk edged out Cup veterans Colin Montgomerie and Padraig Harrington one up in the top match to give the US an early boost.
Spaniards Sergio Garcia and Jose Maria Olazabal hit back immediately after outclassing David Toms and rookie Brett Wetterich 3 and 2 before Briton Paul Casey and Swedish rookie Robert Karlsson halved a pulsating battle with Stewart Cink and first-timer J.J. Henry.
In the final match of the morning, wildcards Darren Clarke and Lee Westwood won a tense battle with Masters champion Phil Mickelson and Chris DiMarco one up to put Europe a point ahead.
It was the closest first session at a Ryder Cup since Europe led the US by the same margin at Brookline in 1999.
Woods, who has won his last five PGA Tour events, was poorly out of touch early on, hooking his first shot of the day into water at the first and putting wildly off the back of the green at the par-four ninth.
But the Americans reached the turn one up with the rock-solid Furyk having birdied the first and also the ninth.
Woods then rattled up successive birdies from the 11th, sinking putts from 12 and 15 feet to put the US duo three ahead before the Europeans cut the deficit by claiming the 14 and 16th holes.
However, both Montgomerie and Harrington missed putts to square the match on the 17th and were unable to do more than halve the last to give the US a morale-boosting start.
"Being in the first group, we wanted to put some red numbers up quick," Furyk told reporters. "Right now we are focusing on trying to win our matches and hopefully build a lead. When you get behind in this tournament, it's tough to get back."
Garcia gave Europe an early advantage in match three by rolling in a 25-foot birdie putt at the par-four first before Cup veteran Olazabal put them two ahead after hitting a superb approach to four feet at the ninth.
Although Toms played well for most of the round, Garcia was in inspirational form and the Spanish duo, who dovetailed superbly, sealed victory at the par-five 16th.
"It's been quite emotional, especially playing with Sergio." said Olazabal after making his first Ryder Cup appearance since Brookline seven years ago.
"I think today there was one secret and that was Sergio. He was just awesome," Olazabal added.
Casey and Karlsson had to settle for a share of the spoils after a battle royal with Cink and Henry.
The Europeans, boosted by a Casey eagle at the par-five fourth, led by three at the turn before the Americans flipped the match on its head with five birdies in six holes from the 10th.
Trailing by one with three holes to play, the hosts leveled when Casey holed a monster birdie putt at the par-five 16th.
In the final match Clarke, whose wife Heather died of cancer last month, sparked one of the biggest roars of the day when he sank an eight-footer for birdie at the first before Mickelson responded with a birdie at the par-five fourth.
Westwood rammed in a 10-footer on 10 to restore Europe's advantage, DiMarco leveled when he sank a curling 25-footer at the 11th but Clarke fittingly secured the emotional win with a birdie at the par-five 16th.