The outstanding Gritton struck a fine hat-trick - taking his tally to five in five games since joining on loan from Lincoln - and defender Alex Baptiste celebrated his 21st birthday with a rare goal as the home side ran riot.
Only desperate defending and several fine stops from keeper Kevin Miller saved the Gulls from the embarrassment of an even heavier defeat.
For United, buoyed by the introduction of nine new players to the club and their first league win in 20 games four days earlier, forced just two saves from home keeper Jason White throughout the one-sided 90 minutes.
The Stags, who replaced suspended striker Barry Conlon up front with Michael Boulding, carved out an early chance for the recalled striker. A swift move down the left wing ended with Boulding cutting inside two defenders before drilling a low drive into the side netting.
At the other end, Jamal Easter's close-range snapshot was well held by the diving White in a fast and furious opening.
Then in the 14th minute Mansfield finally broke the deadlock. First Gareth Jelleyman's cross was headed on by Matt Hamshaw and Gritton's acrobatic overhead kick was tipped over by the flying Miller.
From the following Hamshaw corner, the under-pressure keeper again did well, this time to get a touch on Boulding's powerful ten-yard header but the ball flew into the roof of the net.
Two minutes later a brave block at the foot of the post by Mark Robinson denied Jake Buxton a second goal as the central defender looked to convert another Hamshaw corner at the far post.
With Mansfield in complete control, Hamshaw's 20-yard drive was well held by the diving Miller and then the wingman's looping cross was headed on to the roof of the net by Boulding.
On the half-hour another excellent Miller stop denied the Stags again. Inevitably the threat came from a Hamshaw cross and Baptiste's low finish was superbly blocked by the keeper, who was then fortunate to see the rebound somehow evade the unmarked Gritton.
But luck was against Miller in the 39th minute. After a long, patient build-up, the Stags cleverly worked space on the edge of the area and when Stephen Dawson's mis-hit shot swerved across the area, the unmarked Gritton bundled the ball in from close range.
Torquay, needing a resurgence at the start of the second half, made a double change and almost found a way back when Stephen Cooke's cross caused problems in the home area.
But immediately the Stags regained control of the match and Hamshaw's fierce shot was blocked only by Robinson's last-ditch sliding challenge.
Then more fine defending, this time from Craig Taylor, denied Gritton as he shaped to head in Jelleyman's cross at the near post.
But beleaguered Torquay finally caved in as Gritton started and finished a 59th minute attack. Miller's clearance from outside his area struck Gritton, swirled wide to Boulding, who played in his strike partner to score with a low drive off the post.
Five minutes later makeshift full-back Baptiste struck a rare goal by crashing in a deflected shot at the near post.
Then, after White made only his second save of the night from a Lee Mansell free-kick, the home side went straight back on the attack and grabbed a fifth goal 14 minutes from time.
Boulding was brought down as he raced into the box and Gritton curled the penalty into the top corner to complete his hat-trick.