As American Russell Henley carded a four-under-par 67 to lead in the clubhouse with 36 players still to complete their first circuit, it was also a good day’s work for MacIntyre.
Playing in the afternoon wave, the 24-year-old from Oban carded three birdies and three bogeys as he signed for a 71 to sit in a tie for 24th when play was suspended for the day due to darkness.
His birdies included one from 17 feet at the par-4 10th before rolling in a five-footer at the par-5 18th to sit alongside world No 1 Dustin Johnson, as well as Lee Westwood, Paul Casey and Sergio Garcia.
MacIntyre, who has made the cut in five majors out of five since making his debut in The Open at Royal Portrush, is due out at 3.18pm UK time in his second circuit.
Earlier in the day, Martin Laird, the other Scot in the field, had been near the top of the leaderboard after moving to two-under following an eagle at the 18th - his ninth hole.
However, the four-time PGA Tour winner dropped five shots in six holes at the start of his back nine as he had to settle for a 74 to sit in a share of 78th position.
Henley, who recovered from an opening bogey to card six birdies, shares the lead with South African Louis Oosthuizen, who has two holes to play.
“I feel like I'm a top-50 player in the world,” said Henley, who also shared the first-round lead in his last US Open start in 2018 at Shinnecock Hills. “I've had a ton of top 10s. I've been in contention. I've been really consistent.
“That doesn't mean I'm going to do that the next three days, but I definitely felt comfortable out there.”
Oosthuizen, playing in the afternoon wave, bogeyed the par-4 11th, his second of the day, before covering the next 14 holes in five-under-par.
Should the 2010 Open champion maintain his position or pass Henley when he competes his round later today, it would be the first time he has owned the first-round lead in a major championship.
“I just enjoy playing really tough golf courses,” said Oosthuizen. “I think somehow I focus a little bit better when I play those courses, knowing that the margin for error is really small.
“Especially around this place, you've got to drive it well… and I've really been driving it good lately.”
Two Europeans – 2018 Open winner Francesco Molinari and 2017 Scottish Open champion Rafa Cabrera Bello - shot 68s, while the group lurking two strokes back includes two-time US Open champion Brooks Koepka, hometown favorite Xander Schauffele, Masters champion Hideki Matsuyama and Jon Rahm.
Playing in his first event since having to withdraw from the Memorial Tournament when he was holding a six-shot lead due to testing positive for Covid-19, Rahm recorded his first PGA Tour win at Torrey Pines.
Molinari’s older brother, former Scottish Open champion Edoardo, marked his first appearance in the event since 2011 with a 70 to sit alongside English trio Matt Fitzpatrick, Tyrrell Hatton and Richard Bland.