Neil Harris marked his 300th start for Millwall in perfect fashion with a textbook freekick as Kenny Jackett's men made it five wins in a row to maintain a top six spot.
Harris curled home a sublime 20-yard effort with just nine minutes remaining to finally break through a resilient Exeter rearguard that had successfully managed to repel wave after wave of Millwall attacks.
And no-one played a bigger part in thwarting The Lions than visiting keeper Andy Marriott, 39, who rolled back the years with a vintage display between the sticks.
The evergreen shot-stopper set out his stall in the opening five minutes with two outstanding saves.
Lions striker Steve Morison is yet to score at the North Stand end of the ground, but he is never likely to come closer than the fourth minute of this match. Meeting a delicious Alan Dunne delivery from the right, Morison's fierce header from point blank was somehow tipped over by a stupendous reflex save.
Shaun Batt was denied just seconds later when Marriott again defied gravity - and his advancing years - by getting the slightest of touches to flick the striker's header over for the second of five Lions corners in the first half.
On eight minutes Tony Craig's throw on the left was flicked on by Chris Hackett to Morison, who in turn whipped over a cross that Batt met with a low diving header. That man Marriott was again perfectly placed and comfortably held the ball, as he did once more to frustrate Batt for a third time on the quarter hour mark.
Grecians frontman Marcus Stewart hobbled off injured a minute later, with Bertrand Cozic entering the fray.
Yet the visitors failed to offer much as an attacking threat, seeming content to defend in numbers and bank on trying to catch The Lions on the break, which they certainly failed to do during the opening half.
Harris was a whisker away from connecting with an inviting cross by Batt as Jackett's men tried in vain to find a way through before the break.
The Lions continued to prise and probe in a bid to find a way through, chalking up a stack of second-half chances.
Morison screwed an effort wide after Paul Robinson had flicked on Jimmy Abdou's hooked pass on 47 minutes before the tireless Morison's looping header from Alan Dunne's floated deep delivery was plucked out of the air by the keeper.
That man Marriott came to the rescue again, gathering at the second attempt to avert the danger from Batt with Morison poised to pounce as Millwall kept pressing for that elusive opening goal.
New signing Jon Obika was introduced on 66 minutes for Batt, however it was Exeter who could have broken the deadlock just seconds later.
Sub Stuart Fleetwood latched onto a long forward ball but with just Lions keeper David Forde standing between him and goal glory, he blasted wide of the target.
Fleetwood went close again two minutes later with a cross-shot that dropped just too close to the post for comfort for The Lions as Exeter briefly threatened to get up a head of steam.
With the game entering into the final 10 minutes it looked like it was going to be one of those afternoon's as Morison was left wondering if his side were ever going to score, having seen the ball stick to Marriott's hands on the goalline once more.
Full-back Dunne, who had a fine game both defensively and linking up with Hackett with a string of rampaging attacking runs down the right flank, was involved in a move that came to an abrupt halt when Obika was fouled just outside the area following another mazy run.
It was always going to take something special to beat Marriott - and that's exactly what happened with nine minutes remaining.
Harris and Scott Barron had a quick chat to size up the options, but it was Chopper who took a couple of steps before despatching an inch-perfect free-kick that flew over the wall and into the roof of the net for the 131st goal of his Millwall career.
Matters went from bad to worse for the visitors, who were reduced to 10 men on 88 minutes when Barry Corr was shown a straight red card for a clumsy, rather than malicious, challenge on Dunne.
That effectively ended Exeter's hopes of clawing their way back and they were unable to muster any noteworthy efforts on goal as The Lions held on for a fifth successive win.
Millwall: Forde, Dunne, Craig (Barron, 59mins), Abdou, Robinson, Ward, Batt (Obika, 66mins), Trotter, Harris, Morison, Hackett. Subs not used: Sullivan, Frampton, Grimes, Fuseini, O'Connor.
Booking: Morison (82mins)
Scorer: Harris (81mins)
Exeter City: Marriott, Tully, Duffy, Taylor, Harley, Golbourne, Corr, Edwards, Stewart (Cozic, 16mins (Logan, 83mins)), Sercombe, Burnell (Fleetwood, 59mins). Subs: Jones, J.Dunne, Bennett, Saunders.
Bookings: Tully (81mins), Taylor (81mins), Duffy (83mins)
Sending off: Corr (88mins)
Ref: Phil Gibbs
Att: 9,104 (away 677)