Only three players – Jack Nicklaus (1965-66), Nick Faldo (1989-90) and Tiger Woods (2001-2002) – have won the Masters in consecutive years.
McIlroy is just the seventh Masters champion to have at least a share of the lead at the end of the first round of the following Masters.
Patrick Reed, the 2018 champion, had the fastest start out of the gate with a birdie at No. 1 and eagles at Nos. 2 and 8. He cooled off on the inward nine, making bogeys at Nos. 10 and 15 to finish with 69.
With no rain in the forecast, and fast and firm conditions expected through the weekend, Reed said he expects scoring to become more difficult.
“Just got to be patient. I mean, try to get as many early as you can the first couple of days, because this is one of those golf courses that it can change so quickly,” he said. “With what the weather looks like it’s going to be hot, you know, really hot, sunny, they could make this place really, really hard if they wanted to.”
Jason Day and Kurt Kitayama also joined Reed at 3-under 69.
Justin Rose, three times a runner-up in the Masters, got off to a hot start and was 4-under through 14 holes. Rose, who lost a sudden-death playoff to McIlroy a year ago, bogeyed his final two holes to finish at 70.
Also at 2-under were two-time champion Scottie Scheffler and fellow major winners Xander Schauffele and Shane Lowry.
The group of seven players at 1-under 71 included former Clemson star Jacob Bridgeman, who is making his Masters debut this year.
Many notable players struggled in the first round.
Cameron Young, winner of The Players Championship last month, shot 1-over 73. Ludvig Aberg, a contender the past two years in Augusta, shot 74 after being 3-under through 8 holes. Two double bogeys derailed his day.
Perhaps the biggest surprise was Bryson DeChambeau. The two-time U.S. Open champion, now a member of LIV Golf, played the second nine in 4-over 40 thanks to a triple bogey at No. 11. He finished with 76.