Two months after his suspension ended, he shot a scintillating 65 on day one at Florida's Bay Hill course to top the Palmer leaderboard at seven under.
A two-putt birdie at the par-five sixth moved McIlroy in a share of the lead alongside Talor Gooch, before he grabbed the outright advantage by holing from 15 feet at the par-four eighth and then converted a 10-footer to save par at the last.
With a return to Augusta just a few weeks away, he also said: "I think I've got some good planning for the next few weeks building up to Augusta and some good direction to work towards".
"Anxiety is a real thing and the way I treat it is the healthiest way possible for my body".
"It bothers me that [cannabis] is even an issue [and] on the list of banned substances", he said on Friday (AEDT). This will be Reed's third year in a row playing at the Arnold Palmer Invitational. There's so much trouble out there, especially with the wind. Just because my score was better doesn't mean I'm better than Rory.
OPEC raises stakes with Russian Federation , seeks biggest oil cut since 2008 crisis
OPEC countries such as Saudi Arabia and Iran say they need non-member allies to take 500,000 barrels of that cut on themselves. IHS Markit also said this week that oil demand will likely be lower than in 2019 - even if H2 2020 sees a recovery.
I made a couple of unforced errors starting off.
"I think with the start, then turning in under par with the birdie at 16 and 18, I had a bit of a pep in my step going to the first tee".
Graeme McDowell is 4 under par, with Padraig Harrington 2 over.
McIlroy played alongside Olympic gold medalist Justin Rose of England and South Korean Lee Kyoung-Hoon - a late replacement for defending champion Francisco Molinari after the Italian withdrew with a bad back.
Tenth-ranked Tommy Fleetwood struggled to a 76 and is tied for 107th, while seventh-ranked Adam Scott of Australia came in at 77 and is in a tie for 109th that includes Phil Mickelson, who won this tournament way back in 1997.