A perfect 10 points from Conor McManus helped secure an All-Ireland football quarter-final place for Monaghan, who pulled off the sweetest of revenge missions at Croke Park.
Down had sent Monaghan crashing out of the Ulster championship at the semi-final stage 35 days ago but found repeating that surprise win a bridge too far.
The Mourne County impressed for 45 minutes and were on level terms at 1-11 apiece at that stage in a tight game.
But Monaghan's superior quality and their big-game experience told in the remaining period as they pulled clear with McManus leading the scoring.
Substitutes Conor McCarthy and Jack McCarron kicked six points between them in the last 25 minutes also as Malachy O'Rourke's side moved confidently through to the last eight.
Kieran Hughes was Man of the Match at midfield while his brother Darren, also playing at midfield, had a stormer too.
The win guarantees Monaghan a seventh game in the Championship for the first time in their history. They will face Dublin or familiar foes Tyrone in the last eight.
Popular opinion beforehand suggested that Monaghan, armed with a precious siege mentality after being outfought and out-thought by Down last month, would display their superiority on the grander stage.
For the first five minutes it was panning out that way with Darren Hughes, black carded in their previous win over Carlow, and sibling Kieran kicking them two ahead.
Yet within two minutes Down were back on level terms, setting in motion a tit-for-tat encounter for almost three quarters of the game that was thrilling to watch.
The sides were level five times in a richly entertaining first-half that was notable for Down's utter refusal to go along with the pre-match script.
Down full-forward Connaire Harrison performed superbly on Drew Wylie in Armagh city and was determined to prove it was no one-off.
He did just that with a terrific first-half display and scored three points off Wylie before the Ballybay man was shifted off the powerful Glasdrumman man around the 25th minute.
The third of those points put Down 0-07 to 0-04 ahead with almost 19 minutes played though three converted McManus points for Monaghan tied the game up again.
It was intoxicating stuff, with both sides looking like they would score each time they crossed into the opposition's half.
Fintan Kelly constantly raided forward from his defensive berth and hit an excellent 27th-minute goal, his third in as many games after strikes against Wexford and Carlow.
Darren Hughes and Shane Carey combined to put Kelly free and though Karl O'Connell was free outside him, Kelly opted to fire hard and straight to the roof of the net.
McManus converted his fifth free approaching the half-hour mark and Monaghan were back two clear again, 1-08 to 0-09.
Harrison was to punish Monaghan again though and after beating Kelly in the air to a high ball and laying it off to Dermot Malone was well placed to take the ball on again and slip a shot to the net.
The sides went in deadlocked on 1-09 apiece which just about reflected the back and forth of an intriguing encounter that had the potential to go either way.
Monaghan ultimately seized victory with five points in a row between the 45th and 49th minutes as they opened up with some superb play to move 1-16 to 1-11 ahead.
Substitutes McCarthy and McCarron contributed three of those points and, suddenly, Down looked rattled.
Darragh O'Hanlon had a couple of decent chances for points from Down frees but kicked them wide and shook his head in frustration.
McCarthy, who was held in reserve to allow Darren Freeman, a New York player in 2016, to start in the full-forward line, looked like he had a point to prove.
He kicked his third point to put Monaghan 1-18 to 1-13 ahead in the 58th minute and they remained at least five clear from there on as Down tried in vain to conjure a second goal.
Harrison went close when he broke down a high ball in from the influential Caolan Mooney but his shot flew over as Monaghan finished strong to seal an eight-point win.
Monaghan: R Beggan; F Kelly (1-00), D Wylie, R Wylie (0-01); K O'Connell, C Walshe, K Duffy; K Hughes (0-03, 0-01f), D Hughes (0-03); R McAnespie, D Malone, G Doogan; S Carey, D Freeman, C McManus (0-10, 0-08f).
Subs: O Duffy (0-01) for Malone h/t, J McCarron (0-02) for Carey h/t, D Ward for Doogan 42, C McCarthy (0-04) for Freeman 46, V Corey for Walshe 62, Doogan for McAnespie 69, D Mone for O'Connell 71.
Down: M Cunningham; N McParland, G McGovern, D O'Hagan; D O'Hanlon (0-02, 0-02f), C McGovern, C Mooney (0-01); P Turley, D Donnelly; K McKernan (0-02), C Maginn (0-02), S Millar (0-01); S Dornan, C Harrison (1-04), R Johnston.
Subs: J Johnston (0-03, 0-01f) for Dornan 49, A Carr for Turley 52, M Poland for Maginn 58, D McKibbin (0-01) for Millar 58, D O'Hare for Mooney 68, J Murphy for R Johnston 76.
Referee: M Deegan (Laois)
