The 30-year-old Molinari, who has won two European Tour events, had six birdies for a 29 on the final nine holes at the Sentosa Golf Club.
“My putting was excellent today,” the Italian said. “I holed everything inside 10 feet.”
Mickelson said Singapore’s hot and humid tropical weather may have helped fuel the day’s low scores.
“I think when it’s warm like this the ball flies straighter and it is easier to play,” Mickelson said. “Your muscles feel lose and you swing it much freer and that should equate to lower scores.”
The tournament, marking its 50th anniversary, is using both the Serapong course and the Tanjong course to accommodate 204 players.