Roland Thatcher and Eduardo Herrera share second place at 7-under par, followed by Michael Long, Gary Hallberg, Bubba Watson and Bob Heintz, who are tied for fourth at minus-6.
Allen began on the second nine Thursday and collected two birdies in his first five holes. Around the turn, Allen tallied five birdies in a row from the 17th to get to 7-under for his round.
The 44-year-old from the University of Nevada birdied the par-4 eighth to match the tournament record set by Greg Gregory in last year's opening round when par was 71 and conditions were not contested in lift, clean and place.
'I had a good day on the putting greens,' said Allen, who needed only 26 putts on Thursday. 'When I had some eight-footers, I made them. I made a couple of three and four-footers early for pars. When you're not playing well, you miss those and all of a sudden you're over par.'
Allen has struggled mightily since last year's U.S. Open. He made only one cut in his last 18 starts on the PGA Tour in 2002 and failed to earn his tour card with a 197th place finish on the final money list.
In 2003 on the Nationwide Tour, Allen has made only two cuts in eight starts and his 64 on Thursday was just his sixth round in the 60s so far in the 2003 campaign.
'It's been a long struggle, so it's nice to play one good round,' said Allen, who won the 1998 Greater Austin Open. 'My best score in years is 68, so it's a surprise. It's a nice step.'
Thatcher also began on the second nine, and like Allen, he birdied five holes in a row from the 17th. He mixed in three additional birdies with a bogey for his opening-round 65.
Herrera flew out of the gate Thursday with an eagle and two birdies through his first three holes. He carded back-to-back bogeys at the fifth and sixth and traded a birdie and a bogey through the 13th hole.
Herrera polished off his round with five consecutive birdies to get to minus-7.
Zach Johnson, Stiles Mitchell, Bo Van Pelt and Shane Bertsch share eighth place at 5-under-par 67.