A showdown of global greats at the 7,435-yard Augusta National sees Johnson arrive on a three-tournament win streak.
A showdown of global greats at the 7,435-yard Augusta National sees Johnson arrive on a three-tournament win streak and second-ranked McIlroy, a four-time major champion, seeking a Masters crown to complete a career grand slam.
"I've done all the preparation I can. It's just about going out on the golf course and getting it done," said McIlroy, mindful of 2011 when a back-nine Sunday collapse saw him squander the Masters lead.
"Having a chance to win a few years ago and not giving myself a chance since... internally that's not good enough. I want to give a better account of myself at this tournament and on this golf course and I feel like I can."
Third-ranked Jason Day makes an emotional start two weeks after withdrawing from an event to be with his mother as she battled lung cancer while Jordan Spieth tries to bounce back from a back-nine collapse in last year's final round when on the verge of a second consecutive Masters title.
And five-time major winner Phil Mickelson, two months shy of his 47th birthday, will try to replace Jack Nicklaus as the oldest champion in Masters history.
Forecasts for heavy rain Wednesday to soften the course add to the drama that one of golf's great stages annually produces.
"If it's soft, obviously it will definitely help," long-driving Johnson said. "With the forecast, wind on Thursday and Friday, the course will play very difficult.
"It's going to be tough to hit the greens. You're going to really have to be careful where you hit it and just try to make pars."
That will make a strong start even more imperative than usual.
"It's always important to get off to a decent start but especially here. You don't want to feel like you're playing catch up on this course, because you feel like the more you force the issue, the more things can go wrong," McIlroy said.
"You start to shoot at a few pins... leave yourself in spots you don't really want to. Then you can run up numbers pretty quickly. You don't need to come out and shoot 65 the first day but you're better off shooting something under par."
Johnson enters Augusta after wins at Riviera in February to jump atop the rankings and last month at WGC Mexico and Match-Play events.
"Obviously this year, with Dustin winning three times, he's the form player right now," McIlroy said.
Johnson won his first major title at last year's US Open while McIlroy followed his 2011 Masters heartache by winning the US Open two months later.
"It's never over," McIlroy said. "If I'm four or five behind going into the back nine, it's never over. You can never give up, because it takes either a lapse of concentration from someone else or a moment of brilliance from yourself to turn things around."
McIlroy played 27 holes at Augusta two weeks ago, 54 more last week and 18 more so far this week.
"I've realized the more I get comfortable with this golf course, the environment and the surroundings, the better," he said.
McIlroy has made a believer out of 81-year-old South African legend Gary Player.
"My choice this week -- Rory McIlroy," Player said. "He made a mess of it one year. He has gotten that out of his system and he's playing really well."
Spieth, never worse than second in three career Masters starts, cited McIlroy as an intimidating leaderboard presence.
"When you're paired up, he has been there and you don't feel like you have that major championship winning edge," Spieth said. "That would be somewhat of an edge if it would be mano a mano.
"I don't say I've won the Masters and he hasn't. Trust me, he's certainly capable of it and he'll win at least one. I think if you ask every single player, that wouldn't be a question."