The home side were overwhelming favourites with a 10-6 overnight lead, but saw McDowell three down after five to rookie Jordan Spieth in the opening match and the unbeaten Justin Rose four down after six to Hunter Mahan.
At one point the United States were ahead in six matches, but McIlroy was an approximate eight under par in thrashing Rickie Fowler 5&4 to put the first European point on the board and fellow Northern Irishman McDowell won five out of six holes from the 10th to complete a remarkable 2&1 victory.
With US Open champion Martin Kaymer beating Masters champion Bubba Watson and Rose also fighting back to claim a half, Europe were within sight of victory and Welshman Jamie Donaldson delivered it in style, hitting his approach to the 15th to within inches of the hole to beat Keegan Bradley.
That prompted a handshake on the fairway between captains Paul McGinley and Tom Watson, the former being instantly hailed by his players and the latter certain to be criticised for a number of debatable decisions this week.
One of those was leaving five-time major winner Phil Mickelson on the sidelines all day Saturday, the first time that had happened to the 44-year-old in 10 Ryder Cup appearances.
It was not the only controversy involving Mickelson, who had not been able to resist a sly reference to McIlroy’s court case with his former management company - which has involved current client McDowell - the left-hander responding to queries about American togetherness by saying: “Not only are we able to play together, we also don’t litigate against each other and that’s a real plus.”
McIlroy and McDowell insisted their relationship had been made stronger by the situation and had the last laugh on the course, McIlroy producing easily his best golf of the week to crush Fowler and steady European nerves.
“I was just so up for it, more so than I was in the two majors I won (this year),” McIlroy said. “There was no option other than to win. I played my best golf, six under through six and that built a comfortable lead that I was able to hang on to.”
McDowell, who was disappointed to have played just two foursomes matches before the singles, added: “I’m really proud of myself the way I played the back nine. I’m just relieved, the captain put a big role on me and I’m just happy I could deliver.”
Donaldson had already contributed two points from two foursomes outings with Lee Westwood and was never behind to Bradley, moving four up with birdies on the 11th and 12th and making sure of the half point to retain the trophy with a par on the 14th.
It was only a matter of time before outright victory was confirmed and Donaldson did not disappoint.
“I hit the wedge shot of my life to close the game out. I can’t really put words to it. It is unbelievable,” the 38-year-old said. “I knew it was getting tight there at the end and everyone was building on my group. I just tried not to spend too much time looking at the scoreboard.
“I was able to do it well enough to close it out. The lads have got on so well all week. There has been a great craic in there, it is an incredible week. It is hard to describe how good it is - there is nothing else like it in golf. It has been amazing to be a part of it.”
Europe’s players were quick to praise McGinley, who received public support from the likes of McIlroy, Ian Poulter and Luke Donald when the post was being decided in January 2013.
Sergio Garcia, who beat Jim Furyk on the 18th, said: “He has been so methodical. Every single aspect he needed to touch on, he did. I’ve been fortunate to have a lot of great captains but Paul did things a little bit differently but with great style.
“He has been a little bit more of a modern captain, taking care of every single detail. He knew what we had was good and working but improved it without changing it.”
McIlroy added: “I can’t say enough about the captain. Paul has been absolutely immense this week. He has left no stone unturned. He has given this week a lot of thought over the last two years. I am just glad it worked out for him.”