World number three Luke Donald carded a second- round 71 to trail by five shots at the halfway stage of the Zurich Classic in New Orleans.
The 33-year-old, who can become world number one if he wins this week, began at the 10th and had three early birdies but dropped three shots in two holes.
American Ryder Cup player Bubba Watson added a 68 to his opening 66 to lead by a shot from Josh Teater at 10 under.
US Open champion Graeme McDowell missed the cut after a 75 left him four over.
Northern Ireland's McDowell, who was only one over after the first round despite recording three double bogeys, had four more bogeys and another double bogey in round two but could only post three birdies.
The 31-year-old missed successive cuts at the Arnold Palmer Invitational and the Masters and was tied for 61st at last week's Heritage tournament.
England's Donald, who lost in a play-off at the Heritage which prevented him reaching the top of the rankings for the first time, was relaxed about his position going into the final 36 holes this weekend.
"You're going to make a few mistakes occasionally," he said. "Up until then I played pretty solid golf. Through 29 holes, I only missed a couple greens. But I'm still there or thereabouts and the greens are only going to get firmer. It will be a tough weekend."
Teater, a rookie on the circuit last year, briefly got to 11 under before double-bogeying the last for a 66 and second place in the clubhouse.
On Thursday, left-hander Watson eagled the 11th after hitting a booming 343-yard drive followed by a soaring six-iron over a cypress tree that landed 32 feet from the pin.
A day later he eagled the same hole after sending his tee shot 329 yards down the fairway, striking his second from 244 yards to 20 feet and holing the putt.
"This is what we strive to do," said Watson. "We always want the pressure. We always want the nerves, the butterflies. We're trying to win golf tournaments.
"I've gotten lucky enough to win two so far and I'm trying to go for my third. It would be nice to pull it off here in New Orleans, two-and-a-half hours away from where I grew up.
"I've just putted really well, hit a lot of good tee shots and stayed out of the water as much as possible."
England's Justin Rose, last week's winner Brandt Snedeker, former Open champions David Duval and John Daly all missed the cut.