Haas kept bogeys off his card for a 6-under 66, taking a one-shot lead among the early starters in the Arnold Palmer Invitational. Haas not only hit 15 greens in regulation, he didn't have a putt for par longer than 4 feet.
He was at 9-under 135 going into the weekend, one shot head of John Huh, who had a 66.
Justin Rose, the first-round leader after a 65, and Tiger Woods were among those playing in the afternoon as the temperatures finally warmed.
Haas was challenging for the lead on Thursday until he had to settle for par on the easy par-5 16th. He hit into a back bunker on the par-3 17th for a bogey and finished his round with a three-putt bogey from 8 feet.
"So to leave, basically giving two away, my goal today was try to get those two back and go from there," Haas said. "That was kind of my mindset today, and then I was able to keep it going."
Phil Mickelson won't be around for the weekend. He four-putted from 5 feet on the 13th hole for triple bogey, and whatever hopes he had of making the cut ended when his tee shot sailed left on No. 9 and went out of bounds. Mickelson closed with a triple bogey and a 79, his highest score ever in 48 rounds at Bay Hill.
It was his first missed cut since the British Open last summer.
"There is a huge discrepancy between the low scores and the high scores," he said. "Obviously, I played terrible and I deserved to shoot a score like this. But I felt like if I hit good shots, I could make birdies."
In his five previous years playing the Arnold Palmer Invitational, he had only one round in the 60s.
"I just felt pretty good coming in," he said.
His game felt good. His neck remains a nuisance.
Haas said he hurt his neck while picking up a towel last month, though he referred to it as a sore neck instead of an injury.
"It's not bad," he said. "I can honestly play. I can make a full turn. It's just sometimes when you look to the left it kind of tightens in the back of the neck. It's not anything that's a big deal. When you're playing poorly, it hurts. When you're playing well, it doesn't hurt. It's not so bad. Today it felt good."
Ken Duke (68) and J.J. Henry (67) were at 6-under 138, while the group at 139 included Vijay Singh and Mark Wilson.