"I felt pretty good, the only issue is I hadn't played in three weeks," said Johnson after shooting a first-round 76 on Thursday. "The last time I competed was when I won in Atlanta.
"I'm not doubting my preparation, it's just unfortunate I got sick."
Among the leaders at even par through his first six holes, Johnson then bogeyed four in a row.
"This was a minor shellacking," he said. "You get on a train like that and start thinking about things, you get slapped on the head."
With two more bogeys coming in, Johnson said he felt like the kind of guest Oakmont members prefer.
"Their goal, I've heard, is not to have the guest ever want to come back," he said.
AMES A LITTLE OFF: Stephen Ames, the 2006 Players Championship winner, had one of the more adventuresome rounds. Starting at the 10th hole, he bogeyed two of his first three and shot 3-over on the back nine, made the turn and bogeyed No. 2, then rattled off four birdies in a row to climb back to even par.
Ames then tossed away his momentum with three closing bogeys and shot 73. Later, he said the green speed was "inconsistent," with the greens more exposed to open air much quicker than the greens protected from the wind by trees or large bleachers.
Ames three-putted three times.
EIGHTH HOLE A BIT TAMER: The par-3 eighth hole at Oakmont, which can be played as long as 300 yards, measured at 261 yards in the first round, with the USGA making it shorter due to softer conditions brought on by the rain Wednesday night.
The hole still played the second-hardest on the course at 3.524 strokes per hole. Only four players birdied the hole.
OGILVY FADES LATE: Defending champion Geoff Ogivly bogeyed two of his last three holes to shoot 71, after he trailed by one shot with six holes remaining.
Still, the Australian found a way to shoot a decent number on a day when he needed 30 putts, nearly brained a marshal with his tee shot at the short par-4 17th hole and almost hit his tee shot at No. 12 into a trash bag.