Match ends, Dundee United 1, Aberdeen 0.
Aberdeen's lack of goals is becoming "more and more worrying," says interim manager Paul Sheerin after they failed to score in the ninth time in 10 games.
The Pittodrie club lost at Dundee United in their first Scottish Premiership game since Derek McInnes' departure.
Adrian Sporle's well-worked goal was enough to down the visitors, who have now won just once since January.
"We are always striving to rectify that," said Sheerin.
"I thought a lot of the build-up play was good, but when you are not scoring goals and not getting the end product your play probably deserves it's frustrating."
The defeat leaves Aberdeen in fourth, now seven points behind Hibernian.
The victory for United leaves them in eighth and all but confirms their top-flight safety, given they are 11 points clear of 11th-placed Kilmarnock with just 15 points left to play for.
At kick-off, the home side showed solidarity with Rangers' Glen Kamara by deciding to stand in unison rather than taking the knee.
In a statement, the club said the decision was "to enhance the message that racism in any form is unacceptable and has no place anywhere in society."
After a bright start from United, it was the away side who came closest in the opening stages as a sweeping passing move resulted in Dean Campbell seeing an effort deflected on to a post.
United's Jeandro Fuchs then passed up an opportunity of his own, as the midfielder lashed over Joe Lewis' bar after neat link-up play with Marc McNulty.
But the visitors continued to impress on the counter, playing with an urgency that had been lacking in recent games. Jonny Hayes drove at the United defence before his strike took a nick and curled just past Benjamin Siegrist's near post.
The visitors - with Paul Sheerin in charge - tried to play out from the back, and it worked on the whole for the first period.
There was one near miss, though, when Lewis passed straight to Callum Butcher who fed Lawrence Shankland. The striker composed himself and lifted a delightful dink goalwards, but Ash Taylor was on hand to stop the ball on the line.
However, the Aberdeen backline couldn't prevent Sporle's opener just after the hour.
Fuchs dispossessed debutant full-back Jack MacKenzie on the bye-line before lovely one-touch build-up resulted in Shankland providing for Sporle, who finished low past Lewis into the far corner.
Any attacking flair and zip from the away side faded following United's opener, and confidence dwindled. But Ross McCrorie will be disappointed he couldn't divert a close-range header on target on the closing stages.
Man of the match - Adrian Sporle
What did we learn?
One goal in 10 games is a sobering stat for Aberdeen, but until United's opener, interim manager Paul Sheerin had his players playing a far more vibrant brand of football.
The drop in confidence when they went a goal down shows how much work is there to be done, and now it has to be about consolidating fourth spot and rebuilding for next season.
Mellon might feel disappointed about narrowly missing out on the top six, but Saturday's win all but confirms the Tannadice club's top-flight safety in their first season back in the Premiership.
To be in a position where you don't need to be looking over your shoulder heading into the split - with largely a Championship squad - is good going and gives them a solid foundation for next term.
What did they say?
Dundee United manager Micky Mellon: "It was terrific performance. We've been playing like that for a wee while now. All credit to the players. We keep trying to improve all the time.
"They've grown and attacked everything we've wanted to do. We still believe we can get better."
Aberdeen interim manager Paul Sheerin: "It's disappointing and frustrating. But the players feel it, they worked hard in the 10 days I've worked with them.
"They've been very good so nobody feels it as much as the players do."
It's Scottish Cup action for both sides next on 3 April, as Aberdeen travel to Dumbarton or Huntly and United welcome Partick Thistle or Cowdenbeath.
Their first post-split fixtures will be the following weekend.
- 18ButcherSubstituted forClarkat 90+1'minutes
- 3SpörleSubstituted forAppéréat 84'minutes
- 3HobanSubstituted forRamseyat 90+1'minutes
- 24CampbellSubstituted forHendryat 86'minutes
- 19FergusonBooked at 44mins
- 18McLennanSubstituted forMcGinnat 76'minutes
- 22KamberiSubstituted forHornbyat 86'minutes
- 17HayesSubstituted forKennedyat 86'minutes
- Greg Aitken
- Shots on Target
Second Half ends, Dundee United 1, Aberdeen 0.
Corner, Aberdeen. Conceded by Ian Harkes.
Offside, Dundee United. Nicky Clark tries a through ball, but Jamie Robson is caught offside.
Substitution, Dundee United. Nicky Clark replaces Calum Butcher.
Substitution, Aberdeen. Calvin Ramsey replaces Tommie Hoban.
Attempt missed. Ross McCrorie (Aberdeen) header from the centre of the box is too high. Assisted by Tommie Hoban with a cross.
Corner, Dundee United. Conceded by Ash Taylor.
Foul by Jack MacKenzie (Aberdeen).
Lawrence Shankland (Dundee United) wins a free kick on the right wing.
Substitution, Aberdeen. Fraser Hornby replaces Florian Kamberi.
Substitution, Aberdeen. Matthew Kennedy replaces Jonny Hayes.
Substitution, Aberdeen. Callum Hendry replaces Dean Campbell.
Substitution, Dundee United. Louis Appéré replaces Adrián Spörle.
Jack MacKenzie (Aberdeen) wins a free kick on the left wing.
Foul by Marc McNulty (Dundee United).
Lewis Ferguson (Aberdeen) wins a free kick in the attacking half.
Foul by Ian Harkes (Dundee United).
Foul by Florian Kamberi (Aberdeen).
Ryan Edwards (Dundee United) wins a free kick in the defensive half.