The 10-under par two-day total of Roberts and Perez is one shot better than that of Brian Gay, Bob Tway, Rory Sabbatini, Matt Peterson and Andrew Magee, who are all tied for second at 9-under.
First-round leader Robert Gamez is in a group of eight that includes Mark Brooks, just two back at 8-under.
Also in that group is Garrett Willis who blitzed the course for a course record 61. He had eight birdies and an eagle to shoot up from a tie for 85th.
'It's amazing,' said Willis, who matched the best score on tour this season. 'I just got off to a good start. I birdied the first three holes and just took it from there.'
Roberts' putter enabled the 47-year-old to shoot 31-32 and not a single bogey on the day. His driver also was working well, hitting 13 of 14 fairways.
His last win coming back at the 2000 Greater Milwaukee Open, Roberts hopes to improve on a couple of second place finishes in 2002. He currently stands 46th on the money list.
'I played very well,' said the seven-time PGA Tour winner. 'I missed a bunch of putts yesterday, and I changed my thought process. I made some today by playing less break so I'm going to keep doing that.'
Perez, a leading candidate for Rookie of the Year, was one short of the course record, getting five birdies on the back nine and four on the front. His only bogey, keeping him out of first place all alone, came at his unlucky 13th.
'I'm real pleased,' said Perez, who shot a career-low 62. 'I've been playing well the last three weeks, and I finally got some putts to drop so it's been nice.'
Tway and Gay both shot 6-under 64s to move up the leaderboard following opening round 67s.
Sabbatini backed up his Thursday 66 going one shot better for a 65 that included an eagle and five birdies.
Tom Kite, the 52-year-old Texan enjoyed a 2-under 68 but fell from a tie for ninth into a tie for 25th.
Full-field scores from the Valero Texas Open