The towering target man could have grabbed a record-breaking seventh hat-trick of the season, only to be denied by keeper Willie McCulloch. The Stennies stopper parried Deuchar's 66th minute effort, but substitute Bryan Gilfillan followed up to fire in the rebound for number six.
Stenny had almost taken a shock lead in the fifth minute when Paul McGrillen flashed a low drive inches wide. But Gretna weren't about to have their championship party spoiled, and after skipper Andy Aitken had headed against the post in the 20th minute he climbed highest 10 minutes later to head in the opener from an in-swinging Gavin Skelton free-kick.
The champions made it two four minutes later when Skelton fired in a delightful volley off the underside of the bar.
The champagne was being taken out of the ice box five minutes before the break when Deuchar smashed an unstoppable drive into the top corner from the right angle of the box.
Deuchar grabbed his 38th goal of the season in the 59th minute when strike partner David Bingham sent him clear, and he showed great strength to hold off a challenge and fire low into the bottom corner.
Deuchar turned provider two minutes later when he headed on to send Bingham clear, and he rounded McCulloch to slide home from a narrow angle.
After Gilfillan had added number six, fellow substitute Andrew Smith completed the rout with eight minutes to play when he side-footed home from Ryan McGuffie's screw shot.