Frustrated boss Jimmy Thelin admits Aberdeen blew the chance to finish fourth by being too inconsistent too often this season.
Aberdeen went into the New Firm derby with Dundee United needing a draw to finish fourth and secure a spot in the second qualifying round of the Europa League.
However, Thelin’s Reds threw away a half-time lead to crash 2-1 for a fourth successive Premiership defeat.
The result allowed Dundee United to leapfrog the Dons into fourth place and grab the Europa League prize.
Aberdeen slipped to a fifth-placed Premiership finish and entry to second qualifying round of the Conference League.
In shocking scenes following full-time Aberdeen defender Jack MacKenzie suffered a head wound when he was hit with a chair thrown from the Dons section of supporters.
Loss at Tannadice story of the season
During an ongoing pitch-invasion by United fans, MacKenzie received treatment on the pitch from paramedics. He was then taken off in a wheelchair with his head heavily bandaged.
The full-back received stitches at Tannadice from the Aberdeen medical team.
On the game, Thelin said: “The game in one way summaries a bit the season we have played.
“Dundee United didn’t have to do so much to win the game.
“We started the game well and created chances and controlled situations – but then there were some moments we could not manage good enough.
“That has been the inconsistency through the whole season.
“We have been really, really high and sometimes really good this season, but then we drop.
“Sometimes it can be just for 10 minutes like it was in this game, but it was two goals lost in that time.”
There remains one final European permutation for Jimmy Thelin’s side.
If they beat Celtic in the Scottish Cup final at Hampden next weekend, the Reds would instead enter the Europa League play-offs, with the safety net of dropping down into the Conference League – an outcome far more favourable as it would guarantee extended European action next term.
Boss Thelin searching for solutions
Aberdeen went ahead in the 15th minute against United when on-loan Preston North End winger Jeppe Okkels shot home from six yards.
However, Aberdeen were hit by a double after the break via goals from Declan Gallagher and a Sam Dalby converted penalty.
Aberdeen have now won only two of their last 16 Premiership away matches.
Thelin said: “It has happened before and we have tried to find solutions during the season. That is my job.
“We haven’t found the solution and now we have identified things we have to change for next season inside the club.
“It is about how you manage situations inside the pitch in these moments as a team – how you control the situation after conceding a goal and don’t let the game slip away and take too much time to get back in the game again.
“I’m the manager of this club and it’s my job to try and help the players.”
Three changes after heavy Celtic loss
Thelin made three changes to the starting XI who were hammered 5-1 by Celtic at Pittodrie on Wednesday.
Centre-back Kristers Tobers replaced Alfie Dorrington who was suspended having been sent off against the Hoops.
Thelin also made changes on the flanks with Jamie McGrath and Okkels replacing Shayden Morris and Topi Keskinen.
In the eighth minute, the woodwork denied Aberdeen the opener when a McGrath shot from the edge of the box beat keeper Richards but crashed off the crossbar.
Okkels scores first Aberdeen goal
Aberdeen went ahead in the 15th minute, in a move which was ignited by powerful run down the left flank by Graeme Shinnie.
The Reds captain drilled a low cross along the face of goal to the onrushing Kevin Nisbet, but Richards bravely blocked at his feet.
The loose ball fell to Alexander Jensen, who reacted quickly to square to Okkels six yards out, and he clinically converted with a low right-footed drive for his first Aberdeen goal since arriving in the January transfer window.
In the 40th minute, Dons keeper Dimitar Mitov did well to save a vicious 22-yard low drive by Samuel Cleall-Harding.
Aberdeen dominated the first half, but it all turned soon after the break.
Aberdeen stunned by quickfire goals
Dundee United levelled in the 56th minute when defender Declan Gallagher met a Glenn Middleton corner whipped in from the right.
Ex-Red Gallagher was allowed a free header and directed it into the far corner from 15 yards as Aberdeen’s vulnerability at set-pieces was again exploited.
Aberdeen didn’t react well to the setback and fell behind from the spot in the 63rd minute.
Ryan Strain wend down under contact from Ante Palaversa in the box and a penalty was awarded, which, after a brief check, was confirmed.
Striker Sam Dalby calmly converted, sending Mitov the wrong way.
In injury time, Dundee United keeper Richards produced a superb point blank save to block a six-yard Oday Dabbagh header.
ABERDEEN (4-2-3-1): Mitov 6; Jensen 7, Tobers 6, Knoester 6, Shinnie 6; Clarkson 6, Palaversa 6 (Morris 67); McGrath 6 (Ambrose 75), Gueye 5 (Keskinen 67), Okkels 6 (Polvara 63); Nisbet 6 (Dabbagh 75)
Subs not used: Doohan, Devlin, MacKenzie, Milne
DUNDEE UNITED (4-2-3-1): Richards 6; Strain 7, Gallagher 7, Cleall-Harding 7, Ferry 6; Docherty 6, Sevelj 6; Babunksi 5 (Moult 54), Trapanovski 5 (Paton 54), Middleton 7 (Campbell 88); Dalby 6
Subs not used: Walton, Adegboyega, van der Sande
Referee: John Beaton
Attendance: 11, 490
Man-of-the-Match: Samuel Cleall-Harding (Dundee United)
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