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."
Donald, paired with McIlroy and Westwood, said: "I played pretty solid. I was pleased with my putting - that's always the key for me.
"If I roll it well the rest of it becomes a bit easier."
The up and down pattern of McIlroy's day was established early. He missed the green at the 11th, his second, and bogeyed, but came back with an 11-foot birdie putt on the next.
He almost found the water off the tee at the demanding 18th - Darren Clarke and Sergio Garcia both put two balls in and had triple bogeys there - and dropped another shot, but then almost matched Woods' eagle on the long first.
Then came two bogeys in a row, however, and it could have been worse. His approach to the third hit the rocks by the water, but bounced left and returned to grass.
Woods began as he finished last week with an eagle - it needed only a two-foot putt on the downwind par five first - but that was good as it got.
He birdied two more of the par fives, but had four bogeys.
Paul Casey, playing for the first time since dislocating his shoulder snowboarding on Christmas Eve, returned a 76 - and so did Ian Poulter a week after being diagnosed with pneumonia.
Open champion Clarke showed better form that of late, but only for 17 holes. He came to the last one under, but his horrors there meant a 74.
Garcia's finish completed a day that went from the sublime to the ridiculous. He turned in 31 and was only one behind, but then came home in 44, the triple bogey on 18 following five successive bogeys.
Scott said: "You know it's only a month till the Masters and this is the time you want to knuckle down and get involved."
Bjorn did not have a bogey and said: "When it's this windy you know you need to play solid golf and keep the big numbers off your card. That's what I did."
Collated first round scores in the World Golf Championships - Cadillac Championship, TPC Blue Monster at Doral, Miami, Florida, United States of America
(USA unless stated, par 72):
66 Jason Dufner, Adam Scott (Aus)
68 Charl Schwartzel (Rsa), Thomas Bjorn (Den)
69 Keegan Bradley, Steve Stricker, Aaron Baddeley (Aus), Juvic Pagunsan (Phi), Kyle Stanley, Justin Rose (Eng), Miguel Angel Jimenez (Spa), Alvaro Quiros (Spa)
70 Zach Johnson, Anders Hansen (Den), Bubba Watson, Charles Howell III, Peter Hanson (Swe), Paul Lawrie (Sco), Luke Donald (Eng), Johnson Wagner
71 Hunter Mahan, Nick Watney, Gary Woodland, Greg Chalmers (Aus)
72 Tiger Woods, David Toms, Matt Kuchar, Mark Wilson, Phil Mickelson, Fredrik Jacobson (Swe), Jbe Kruger (Rsa), Martin Laird (Sco), Jonathan Byrd, Y.E. Yang (Kor)
73 Hennie Otto (Rsa), Garth Mulroy (Rsa), Nicolas Colsaerts (Bel), Geoff Ogilvy (Aus), Martin Kaymer (Ger), Jason Day (Aus), Ben Crane, Rory McIlroy (NIrl), Bo Van Pelt
74 Retief Goosen (Rsa), K.t. Kim (Kor), Tadahiro Takayama (Jpn), Darren Clarke (NIrl), Simon Dyson (Eng), Alexander Noren (Swe), Bill Haas, K J Choi (Kor), Gonzalo Fdez-Castano (Spa), Rickie Fowler
75 Francesco Molinari (Ita), Graeme McDowell (NIrl), Sergio Garcia (Spa), Webb Simpson, Robert Karlsson (Swe), Dustin Johnson, Vijay Singh (Fij), Robert Rock (Eng), Rafael Cabrera Bello (Spa), Brandt Snedeker
76 Paul Casey (Eng), John Senden (Aus), Ian Poulter (Eng), Marcus Fraser (Aus), Lee Westwood (Eng), Pablo Larrazabal (Spa)
77 Louis Oosthuizen (Rsa)
78 Tetsuji Hiratsuka (Jpn), Branden Grace (Rsa), Chez Reavie
79 Sang-moon Bae (Kor)