I didn't get going - McIlroy
Rory McIlroy admitted to being "mentally flat" as he began his reign as world number one.
The 22-year-old from Northern Ireland managed only a one-over-par 73 at the start of the season's second world championship in windy Miami.
McIlroy said: "All of a sudden you're there (top of the rankings) and you're like 'Well, what do you do?' I just need to go out and set myself a target tomorrow."
He is seven behind Cadillac Championship pacesetters Adam Scott and Jason Dufner and perhaps the only crumb of comfort was that Lee Westwood, who like Luke Donald (70) could take the number one spot back with victory, handed in a 76.
While McIlroy was winning the Honda Classic on Sunday, Westwood was charging into fourth place with his best-ever round in America - a 63 - but this time the 38-year-old bogeyed his first three holes and finished near the rear of the 74-strong field.
Australian Scott, already with a world title to his name, and American Dufner, runner-up at the USPGA Championship last August, led by two from Dane Thomas Bjorn and Masters champion Charl Schwartzel, while the leading British player was Justin Rose after a 69 - one better than Donald and Scot Paul Lawrie.
As for Tiger Woods, second to McIlroy in Palm Beach Garden following a career-low finishing round of 62, he shot 72 like Phil Mickelson.
McIlroy added: "There's going to be times where you're going to feel a little bit off and it's just trying to handle those the best you can.
"I was mentally flat and it was a bit of a struggle. It was a pretty tricky day, but obviously there was good scores out there. I just didn't really get anything going.
"After what happened last Sunday - Tiger shoots 62, I end up winning to go to world number one - obviously people are going to talk, but I think everyone has to remember that there's 80 other players in this field or whatever it is and it's not just about a couple of guys."