Rich Beem, the 2002 PGA champion, and Olin Brown share second place at 7-under-par 64. Jeff Sluman was one shot further back at 6-under-par 65.
'I shot 13-over on Sunday and 10-under today, so that's a big swing,' said Howell, who posted an 83 in the final round of the U.S. Open at Shinnecock Hills. 'I don't reckon I've had a 23-shot swing in two rounds of golf.'
Howell, who celebrated his 25th birthday on Sunday, jumped out of the gate with a birdie at the 10th, his first. Howell then hit his tee shot to 15 feet for a birdie at the par-3 11th, but gave that shot back with a bogey at the 12th.
He responded with back-to-back birdies starting at the par-5 13th, but faltered again with a bogey at the par-4 15th to make the turn at 2-under.
If the back nine was a bit of a roller coaster for Howell, the Augusta native had to hold onto his hat with the scoring that awaited him on the front side.
'It was one of those funny days where everything tends to work your way, and the best that you can do is get out of the way and just let it continue to happen,' he said.
Howell tallied an eagle at the par-5 second and hit his approach to ten feet for a birdie at the par-4 fourth. He kept on rolling with a birdie at the fifth and sent his second shot to the par-5 sixth within 15 feet of the hole.
Howell converted for eagle and played his approach to 30 feet for a lengthy birdie at the par-4 seventh.
At the par-4 eighth, Howell continued the putting display with a 20-footer for another birdie. Howell had a long birdie putt left at the ninth, but could not convert. Despite the closing par, Howell came in with a 28 on his way to a new course record at the TPC at Avenel.
'The best way to describe it is you get a feeling that you can do nothing wrong, and it's just a feeling that no matter what you ultimately are deciding to do, no matter what happens, you have a feeling and a knowing inside of you that you can't do anything wrong,' said Howell, whose lone PGA Tour win came at the 2002 Michelob Championship at Kingsmill. 'How to recreate that feeling, obviously is the $64,000 question. But is sure is fun when it does happen.'
Beem, who missed the cut last week at Shinnecock, was also on fire Thursday with six birdies over his first nine holes.
The 33-year-old, who captured this event in 1999, dropped his second shot to four feet for a birdie at the 10th to move to 7-under. Beem cooled down from that point on with a birdie and a bogey for his share of second.
'I played solid all day,' said Beem. 'I mean, what could I say? I came back to a golf course that I love to play every year and got off to a really good start.'
Adam Scott, Billy Mayfair, Scott Hend, Tom Lehman and Blaine McCallister shared fifth place at 5-under-par 66.
Defending champion Rory Sabbatini was one shot further back in a group at 4-under-par 67.