Far from finished with his Augusta wizardry, the American then holed-out for another birdie at 17 after chipping in from off the green.
Day, who has battled back injuries over the previous year, re-injured his back picking up his daughter while on the practice green, according to ESPN.
Dustin Johnson and Ian Poulter were at 68, and Jon Rahm and Adam Scott were among those at 69.
They were one shot ahead of 48-year-old Phil Mickelson, who had his best start at the Masters since 2010, when he won his third green jacket.
The projected cut line for the Masters is three-over-par given Augusta still uses the rule that those within 10 shots of the lead advance to the weekend rounds.
Luke Walton out as LA Lakers coach after three losing seasons
The Los Angeles Lakers and coach Luke Walton have agreed to part ways, the team announced on Friday afternoon (April 12). The Lakers finished this season 37-45 and have failed the reach the playoffs over the last six seasons.
He had not broken par at the April major since the 2014 edition but birdied the final two holes and briefly shared the clubhouse lead with South Africa's Justin Harding and Rahm.
It is reported he aggravated his chronic back injury by picking up one of his children on Thursday morning although that hasn't been confirmed.
British Open champion Molinari, who began the day four shots back of the overnight leaders, carded four birdies through an error-free 12 holes at an overcast Augusta National to move to six-under.
Marc Leishman is at even par after three-putting the last hole for a bogey.