The young Scot found himself one down with six holes to play at Austin Country Club before a chip-in eagle from 30 yards at the 13th, a 30-foot birdie putt two holes later then another eagle from a bunker at the par-5 16th helped him secure a 2&1 success.
“It was one of the best matches I've been involved in,” admitted MacIntyre of his brilliant start to the $10.5 million event. “Both of us were playing really well, we weren't giving an edge then just the last five holes just we both started going crazy.
“I chip in when he's knocked it in tight, and it just kind of fed from that. The confidence was there on my game all day, and I just continued to just commit to the shot, and it paid off at the end.”
In a round-robin format, MacIntyre now takes on world No 1 Dustin Johnson, who wasn’t firing on all cylinders as he beat fellow American Adam Long by two holes.
“Yeah, it's huge for confidence,” said MacIntyre of his win heading into the clash with Johnson.
“I'm really starting to trust what I'm doing and I'm starting to see shots and hitting the shots that I'm trying to hit.
“That's huge when you're trying to play match play and trust what you're doing, and even if you get behind, you've got to keep trusting it. Yeah, just looking forward to seeing what happens tomorrow.”
Johnson, who defends his Masters title in a fortnight’s time, was two up with seven to play before surviving a wobble against Long.
He said of meeting MacIntyre: “I know he's a good player. I don't know him that well, but it'll be a good match.”
Earlier, Rory McIlroy hit a wayward shot into a swimming pool as he joined Bryson DeChambeau in tasting defeat on the opening day of the $10,5 million event.
McIlroy’s first competitive outing since adding Pete Cowen to his coaching team didn’t deliver the galvanising effect he was looking for as the Northern Irishman crashed to a 6&5 defeat against Ian Poulter.
McIlroy, who missed the cut as defending champion after an opening 79 in the Players Championship at TPC Sawgrass earlier in the month, was already two down when his tee shot at the fifth went out of bounds and ended up in a swimming pool.
Poulter, Europe’s Ryder Cup talisman, looked to have a game on his hands when McIlroy got it back to one down after eight before the Englishman won the next five holes on the spin, clinching victory as his opponent chipped into the water across the green at the 13th.
“I’m not sure it was easy, to be honest,” said Poulter of his comprehensive success. “I mean, you’re playing Rory and it was apparent when you’re one up after being three up that this is not going to be an easy match.”
Poulter carded an eagle and three birdies in his match-winning burst, adding: “I played well and obviously the score line's pretty flattering, to be honest. But I kept Rory under pressure and I made it difficult for him.”
Due to the round-robin format, McIlroy can still qualify for the knock-out stage, as can world No 2 Justin Thomas and US Open champion DeChambeau after they also suffered opening-day defeats.
In his first outing since winning the Players Championship, Thomas went down 3&2 to fellow American Matt Kuchar while DeChambeau lost by two holes to Frenchman Antoine Rozner, who only got into the event on the back of his Qatar Masters victory earlier in the month.
“I'm very happy,” admitted Rozner, who was three up with six to play before staving off a fightback from his opponent. “I was starting to feel a little bit nervous on the back nine,” he added.
Rozner became the fastest Frenchman to rack up two victories on the European Tour, having made his breakthrough in the Golf in Dubai Championship in December before completing a Middle East double by holing a 60-foot birdie putt on the final hole in Qatar in just his 29th start on the circuit.
“I played a lot of match play as an amateur,” he said after this success. “I won the French Am back-to-back. I played the Palmer Cup as an amateur and won my four matches there, so I've got a pretty good record in match play.”
Dundee-based Victor Perez added to a great day for French golf as he dug deep to beat the stuffy Australian, Marc Leishman, 2&1.
“I’m very happy as he is a tough customer,” said Perez, who has emerged as a strong contender for this year’s rescheduled Ryder Cup after going from strength to strength since winning the 2019 Alfred Dunhill Links Championship.
Defending champion Kevin Kisner beat 2010 Open champion Louis Oosthuizen while other winners included Spanish duo Jon Rahm and Sergio Gercia, who was six-under for 15 holes against Lee Westwood, and Texan Jordan Spieth.
The latter defeated Matt Fitzpatrick while other Europeans to taste defeat included two-time beaten finalist Paul Casey, Open champion Shane Lowry, Ryder Cup contender Viktor Hovland and 2018 Scottish Open champion Bernd Wiesberger.
Full first-day results
Dustin Johnson bt Adam Long two holes
Kevin Na lost to Bob MacIntyre 2&1
Justin Thomas lost to Matt Kuchar 3&2
Louis Oosthuizen lost to Kevin Kisner 2&1
Jon Rahm bt Sebastián Muñoz one hole
Ryan Palmer bt Shane Lowry 4&2
Collin Morikawa halved with J.T. Poston
Billy Horschel bt Max Homa one hole
Bryson DeChambeau lost to Antoine Rozner two holes
Tommy Fleetwood halved with Si Woo Kim
Xander Schauffele halved with Andy Sullivan
Scottie Scheffler bt Jason Day two holes
Patrick Reed halved with Bubba Watson
Joaquin Niemann halved with Christiaan Bezuidenhout
Tyrrell Hatton halved with Matt Wallace
Lee Westwood lost to Sergio Garcia 4&3
Webb Simpson bt Talor Gooch 6&5
Paul Casey lost to Mackenzie Hughes 3&2
Patrick Cantlay bt Brian Harman one hole
Hideki Matsuyama lost to Carlos Ortiz 4&3
Rory McIlroy lost to Ian Poulter 6&5
Cameron Smith bt Lanto Griffin one hole
Tony Finau lost to Dylan Frittelli 6&5
Jason Kokrak bt Will Zalatoris one hole
Viktor Hovland lost to Kevin Streelman 4&2
Abraham Ancer bt Bernd Wiesberger 3&2
Daniel Berger bt Erik van Rooyen 6&4
Harris English bt Brendon Todd one hole
Matt Fitzpatrick lost to Jordan Spieth 3&1
Matthew Wolff bt Corey Conners 3&1
Sungjae Im bt Russell Henley one hole
Victor Perez bt Marc Leishman 2&1