Aberdeen cemented their place in next season's Europa League with what was an emphatic win in a compelling game that brought a controversial red card for Barry Robson, the Dons veteran midfielder.

The former Dundee United player was left dumfounded as referee Bobby Madden judged he had used his arm into Charlie Telfer's face as the pair battled for the ball deep in the home side's half and they were left to play-out the remaining twenty minutes clinging to the lead they'd taken with Adam Rooney's first-half strike.

There were no post-match histrionics from Derek McInnes, the Dons manager, over the incident, however, though he felt the decision was harsh.

"I think there was a coming together," he insisted, "but at no time did I see Barry elbow anyone. I've watched it again on DVD and I don't think there was a red card offence there. The linesman is far closer than I was, though.

"It's disappointing because for me it wasn't clear that Barry has done a lot wrong. It was a harsh decision but I don't want it to detract from a great result. It's great to be in Europe with five games to go and we need to go on a clinch second place now. The consistency has been good but we still have work to get on with. We want to pick up as many points as possible and it's pleasing to see the players so determined to pick up as many points as we can."

McInnes, keen at this stage of the season to freshen-up his side, recalled Ash Taylor to defence and Robson to strengthen the midfield, as Donervorn Daniels and Cammy Smith took their places among the substitutes.

United had brought a poor 10-game run to and end with a narrow and fortunate win against Hamilton last weekend but still made changes. Jaroslaw Fojut returned to a three-man defence while Calum Butcher and Mario Bilate were also offered stars, replacing the injured Paul Paton, Blair Spittal and Aiden Connolly, who was ill.

There was a predictably high tempo to this game and with it a certain tension. But it took until the 14th minute before there was any real sign of a breakthrough. Kenny McLean's superbly-weighted diagonal 40-yard pass found Jonny Hayes on the left and, as the Dons winger raced-in on goal the manoeuvre ended as Radoslaw Cierzniak's long legs blocked the shot, the keeper continuing the form he showed seven days earlier when he was outstanding against Hamilton.

Twelve minutes later, with Aberdeen producing attractive, attacking football, another chance fell for Hayes, this time as Fojut failed to deal with Shay Logan's lob into the area, and the Irishman was just short in making contact at the back post.

It was a similar move that brought reward seven minutes from the break, though on this occasion it was Robson's searching ball that was touched on at the back post by Mark Reynolds to Adam Rooney, standing alongside him, and the striker hit his 27th goal of the season, 17 of which have come in league football.

The visitors would have drawn level five minutes later had Bilate taken his chance yards from the Aberdeen goal, but Brown's block rescued the Reds.

The Arabs looked livelier at the beginning of the second phase, despite Bilate being forced to retire with a hamstring injury after a minute's play, but a piece of sloppiness from their defence presented man-of-the-match Willo Flood with space and time to hit a stinging 27-yard strike, prompting an acrobatic save from Cierzniak.

But it was the touchline incident 20 minutes from the end when Robson was ordered off that threatened to change the course of this game as Telfer hit the ground complaining that his features might have been rearranged because of the Aberdeen midfielder's arm into his face. Meanwhile, the home side introduced Jack for McGinn, determined they would not surrender their lead.

"A lapse in concentration has cost us," said Jackie McNamara, the Tannadice manager, "and that's why Aberdeen are second in the league just now.

"There's wasn't much in the match. But we didn't cause Aberdeen enough problems when they went down to 10 men. That was disappointing. They were streetwise, experienced and strong. That's why we couldn't afford to concede set-pieces."

"We've lost concentration and it has cost us. That has been the story recently, but winning games is what breeds confidence. To get that back, we need to start winning games and keeping clean sheets."

Aberdeen (4-2-3-1): Brown; Logan, Taylor, Reynolds, Considine; Flood (Daniels 90), Robson; McGinn (Jack 74), McLean, Hayes; Rooney. Subs not used: Langfield, Smith, Pawlett, Goodwillie, Shankland. Booked: Sent off: Robson 70.

Dundee Utd (3-4-2-1): Cierzniak; Fojut, Morris, Souttar; McGowan, Telfer, Butcher (Coote 76), Dixon; Ciftci, Erskine; Bilate (Muirhead 47). Subs not used: Szromnik, Dillon, Spittal, Smith, Anier. Booked: Ciftci 37, McGowan 57.

Referee: B Madden.

Attendance: 12,619.

Man of the match: Willo Flood.