Weibring, whose best finish this season was a third-place in the MasterCard Championship, the opening tournament on the Champions Tour, had six birdies and an eagle at the Del Monte Golf Course.
'I've been playing well lately,' Weibring said. 'It was a bonus to birdie the two par 3s on the front nine, and I played a little more conservatively off the tee than usual.'
Weibring completed his bogey-free round with a 20-foot birdie putt, the longest of his round, on the 392-yard 18th. He completed the front nine with an eagle 3 after he hit his 3-wood second shot within three feet.
'We had a nice morning to play,' Weibring said. 'I don't feel like I've putted well all year, but my caddie has been working with me and we're developing a good chemistry now.'
Purtzer, who has four top-10 finishes this season but is also winless, carded his 66 at Del Monte. Haas, second on the money list to Loren Roberts and vying for his fourth title of the season, carded a 66, the low round at Pebble Beach Golf Links.
David Eger, Scott Simpson, David Edwards, Tom McKnight and Roberts, the Champions Tour money list leader, all shot 67s.
Defending champion Hale Irwin, who has won on the either the PGA Tour or Champions Tour every year since 1993 but is winless this season, shot a 1-under par 71 at Del Monte.
Gary Player, age 70, shot a 69, also at Del Monte. It marked the fourth time in his career Player has posted a score lower than his age. The uniquely formatted tournament features Champions Tour players grouped with a youth golfer and two amateurs.
The Champions Tour players compete for $2 million, but there are also two best-ball competitions. The tournament continues through Sunday's final round at Pebble Beach. The winning pro earns $300,000.