Day singled in the first, walked in the second, tripled in the third, doubled in the fourth, doubled in the fifth and walked in the sixth.
An early lead helped set the Mariners on the road to victory at Central Park.
The Plymouth side scored with a single by Martin Mules and Day in the first innings.
Mules added another single in the second innings to add to walks by Dan Brown, Day, Kaz Rahman in the second inning and singles by Matt Vann and Greg Staniforth.
Plymouth Mariners scored eight runs in a big third innings, thanks to a triple by Day, a double by Vann, a single by Staniforth, a walk by Daniel Herrera and a double by Day.
Bristol Badgers, though, replied with four runs in their third innings.
But Plymouth continued to impress. Day, Mules, Herrera, Vann, and Staniforth each collected multiple hits for Plymouth Mariners.
The home team also tore up the base paths, as five players stole at least two bases. Mitch Prescott led the way with five.
The Mariners have won three of their opening four fixtures this season.
Other South West Baseball League results: Bristol Bats 17 Newton Brewers 0, Taunton Muskets 4 Exeter Spitfires 3, St Austell Claycutters 17 Taunton Musketeers 16