Glentoran took full advantage of a partied-out Cliftonville as they claimed a 3-0 win over the newly crowned champions.
Despite the win, Eddie Patterson's men have a long way to go before proving themselves as more than just competition for the Reds when the team meet again in next month's Irish Cup final.
Andy Waterworth struck twice in the first 12 minutes to give the home side an early advantage, after an attacking flurry from the new Danske Bank Premiership champions.
Reserve product Carl McComb then grabbed a third in the second half, coming off the bench in the 76th minute and scoring within a minute.
Stephen Garrett and Martin Donnelly had three strong chances between them, but the Glens soon identified a sluggish, weary midfield and played the Reds at their own game.
Speaking after the game, Glentoran boss Patterson said: "This season, we have a different Glentoran.
"We had a couple of players injured and a couple suspended ourselves, and obviously out there you saw two different teams which will come out on cup final day, but both teams were fundamentally after three points, I think, irrespective of Cliftonville winning the league.
"Of course, we're delighted with the win. We got two good goals from Andy, who has done that all season.
"There were some really good performances from some of the younger lads, we have some good lads working hard every week, but competition for places still applies now and it will apply until the end of the season."
Waterworth hit a stunning shot from 25 yards out on nine minutes, after collecting it in his own half from Elliott Morris' distribution.
He beat deputy goalkeeper Ryan Brown for a second time three minutes later, escaping a challenge from Ciaran Caldwell to rifle home from an acute angle.
He almost rounded off a hat-trick when he was through on goal before Dermot McVeigh intercepted.
Cliftonville looked disinterested and unwilling to produce a reaction. David Howland located Richard Clarke in midfield, who crossed to Martin Murray who blasted wide.
At the other end, Garrett set up Tomas Cosgrove, whose effort was saved by Morris.
Tommy Breslin had named an almost completely different side to the starting 11 which buried 15 years of frustration, winning their first league title since 1998.
What will have frustrated him from last night's pedestrian show, was how few of those seven changes looked as if they wanted to show their worth for a place in May 4 final.
The nearest they came was on 64 minutes when Donnelly's curling free kick was punched away by Morris.
Anthony McConnell was thrown on for Caldwell two minutes later to throw his weight around in an advanced role, while Anthony O'Hanlon's fresh legs were just as desirable up front, hassling the Glens late on.
McComb, replacing a lacklustre Stephen Carson, then toe-poked the ball in behind Brown for his second goal of the season.
GLENTORAN: Morris, Kane, (McCullough, 75), R Clarke, Ward, Howland, Waterworth, Carson, (McComb, 76), M Clarke, (Bradley, 66), Callacher, Murray, Birney, Subs: Nixon, Gibson.
CLIFTONVILLE: Brown, Caldwell (McConnell, 65), Garrett, (O'Hanlon, 57), Donnelly, Seydak, Lynch, Stuart, Cosgrove, McVeigh, Knowles, McGovern (Reynolds, 75). Subs: Smyth, McGrandles.
Referee: R Hetherington (Dungannon).