With his team needing a fast start to the third session of play at Hazeltine, the Northern Irish world number three dovetailed superbly with Belgian rookie Thomas Pieters as they completed a 4 and 2 victory over Mickelson and Rickie Fowler.
The duo inspired a thrilling display by their team on a gorgeous morning of unbroken sunshine in Minnesota, with Europe winning two-and-a-half points out of a possible four against the United States to reduce the overall deficit to 6 1/2 - 5 1/2.
For McIlroy, his victory in tandem with the long-hitting Pieters had an added bonus as it was the first time in four attempts he had beaten U.S. veteran Mickelson at the Ryder Cup.
"When I saw the draw last night, I was like, 'Yes, I get to have a go at him (Mickelson) again', because my record against him in the Ryder Cup isn't what I would like it to be," McIlroy told reporters.
"Thankfully I was able to get one back on him. Personally, I may be wanted it a little bit more just for that reason but to go out first and put a point on the board for Team Europe, that's what we wanted to do."
McIlroy, along with fellow Northern Irishman Graeme McDowell, lost to Mickelson and Keegan Bradley in a fourball match at Medinah in 2012.
In partnership with Spaniard Sergio Garcia, he lost to the same U.S. combination in the opening fourball encounters at Gleneagles in 2014.
In Friday's opening foursomes at Hazeltine, McIlroy and England's Andy Sullivan were beaten by Mickelson and Fowler after they had been 2-up after 14 holes.
On Saturday, however, he and Pieters clicked in their first alternate-shot match together, piling up six birdies in 16 holes to win comfortably against error-prone opponents.
While the U.S. have approached their matches with a fine attention to detail, McIlroy and Pieters took a more casual approach.
"We had not really practised (in the foursomes format)," McIlroy said. "We had not chosen what golf ball to play, had not chosen what even tee to go off.
"We flipped for it on the first tee, but it seemed to work out pretty well."
(This version of the story corrects the number of McIlroy-Mickelson matches in paragraph four)
(Editing by Andrew Both)
