Forsman had eight birdies and a bogey in the opening round on Rock Barn Golf and Spa's Jones Course. He won the season-opening Mitsubishi Electric Championship in Hawaii in January for his third Champions Tour title.
The 54-year-old player pulled a back muscle two weeks ago.
"I hadn't struck a ball until (Thursday)," Forsman said. "I've been able to spend a lot of time on the putting green, and that paid off. I knew I had to play sensible because I had my limitations ... but my momentum built up once I made some putts. It was fun. I enjoyed the heck out of it."
Frost and Mize had bogey-free rounds, and Funk had four birdies and a closing eagle on the par-5 18th.
"I had a few opportunities early that I didn't make," said Funk, who won at The Woodlands in Texas in May for his seventh Champions Tour title and first in nearly two years. "But it turned out to be a good day."
"That ace on No. 3 was just lucky," Wiebe said. "I didn't even know it had gone in. I heard some people cheering on the green, but I thought that was because I had hit it close."
Last week, Forsman had a second-round 80 and finished 78th at 10 over.
"I'll tell you how bad it was (last week) ... on the ninth hole, I had a spasm so bad I hit the deck," Forsman said. "My son (Tommy) had to help me up so I could finish the round."
After the final two regular-season events, the top 30 on the money list will advance to the Charles Schwab Cup Championship on Nov. 1-4 at Desert Mountain in Scottsdale, Ariz. Forsman is 24th with $568,519.
"This couldn't have come at a worse time, because I'm trying to make the Schwab Cup," Forsman said. "I've got a lot riding on that personally, so I'm grateful to be able to come out here and play as well as I did today."