Russel Henley shot a 4-under-par 67 to grab the lead in the slow-moving first round on Thursday at Torrey Pines in San Diego.
South Africa's Louis Oosthuizen is also at four under, but he still has two holes to complete as the first day's play was suspended due to darkness.
Oosthuizen was among three dozen players unable to complete the round due to a morning fog delay of 90 minutes.
Francesco Molinari of Italy and Rafa Cabrera Bello of Spain were at three-under in the third major of the 2020-21 PGA Tour season.
The talented Xander Schauffele, two-time U.S. Open winner Brooks Koepka, reigning Masters champion Hideki Matsuyama and pre-tournament favorite Jon Rahm finished their rollercoaster day at two-under.
McIlroy, running from the fairway to the green in the fading light, birdied 18 to reach one-under to sit inside the top-11 spot at the leaderboard.
Jon Rahm also raced to finish and also birdied his final hole to claim tied fifth position.
Defending champion Bryson DeChambeau finished his first round at two-over. He was saved by two birdies across the last five holes after a stretch of three straight bogeys.
Phil Mickelson, who won last month's PGA Championship, had just one birdie and finished four over.
The 36 players, who didn’t finish, some with as many as six holes left, will resume play beginning at 6:50 a.m GMT-4. Friday, June 18.Posted on: 2021 Jun 18 Fri