Pavin shot a 9-under 61 after making the turn with a nine-hole PGA TOUR-record 26. He birdied eight of the first nine holes on the par-34 front side of the Brown Deer Park Golf Course.
Chris Smith shot a 7-under 63, Jerry Kelly and Arjun Atwal opened with 64s and five other players shot 65 at one of the shortest courses on the PGA TOUR at 6,759 yards.
The 46-year-old Pavin, who had a bogey-free first round, left just three minutes before severe thunderstorms stopped play for the day Thursday.
That meant many golfers were forced to return early Friday morning, including 54 who hadn't even started their rounds. Defending champion Ben Crane had only made one shot before play was halted Thursday, and finished the first round at 3-under 67.
Smith played just three holes on Thursday, and started Friday with birdies on four of his first five holes.
'I think half of it is you've got to convince yourself you got the good break,' Smith said Friday before taking about an hour break before teeing off for the second round.
Kelly, of Madison, Wis., was enjoying the hometown support.
'The people here don't let me get down on myself,' he said. 'After a bad shot, you get mad after the hole, but when I finish, they are right there cheering me on.'
Pavin, who won the U.S. Open in 1995, managed only one birdie on the final nine holes and admitted that he was nervous because he was close to the mark of 59, which is the PGA TOUR's scoring record for a round.