McGlashan's first-half opener capped a fine display from the midfielder, who signed from Aldershot in January, while Burgess' measured header put the Gloucestershire side in pole position for the Wembley final.
Torquay, beaten play-off finalists last season, settled quicker than their hosts and Rene Howe fired an early effort just over the bar.
Martin Ling's side narrowly missed out on automatic promotion and finished four points above the hosts but found goalkeeper Scott Brown in inspired mood.
He rushed out to deny Ryan Jarvis as the Walsall loanee looked to lift the ball over him from 12 yards out.
The home side were given a scare from the subsequent corner, which Brown badly misjudged to set up a goalmouth scramble from which Lee Mansell shot wide.
Mark Yates' men reacted well and imposing striker Burgess' header was tipped over by Robert Olejnik in the 18th minute.
The visitors then suffered a significant setback as Howe went off injured, Ling watching his 14-goal top scorer leave the action midway through the first half.
The breakthrough came soon after to compound Torquay's misery. Damon Lathrope conceded possession in midfield, allowing Luke Summerfield to feed McGlashan, who darted into the area and slotted home via the far post.
The goalscorer then took a whack to the face from an attempted clearance, leaving him groggy for a few minutes and it seemed to affect his balance when, moments later, he ran clear down the right wing only to fall over as he tried to deliver a cross.
Mansell's overhead kick dropped wide of the far post in Torquay's final attack of the half.
An action-packed start to the second half saw both sides strike the woodwork and the Robins double their advantage.
First Mark Ellis tried to poke Summerfield's cross behind for a corner but smashed the ball against the post, then Burgess directed a powerful header into the top corner from McGlashan's cross.
Jarvis spurned a glorious chance to reduce the deficit almost immediately as he headed against the bar from close range.
Substitute Taiwo Atieno tested Brown with a late toe-poke and a back-post header but could not find a way through, leaving Torquay with a two-goal deficit to overturn in the second leg at Plainmoor on Thursday.