Ally McCoist last night asked Rangers supporters to be open-minded about Bill Miller's takeover bid as the American and the Blue Knights endured another day without receiving preferred bidder status from the club's administrators, Duff & Phelps.

Some fans' demonstrations had been expected against Miller at Ibrox but none materialised. The message from within the club itself was clear: it would be dangerous to turn on Miller and scare him away when Rangers' survival was so fragile.

"We have to be supportive of someone who, hopefully, could come in and take the club forward," said McCoist. Supporters are suspicious of Miller, perceiving his bid to be about liquidation and a newco whereas The Knights and Brian Kennedy want to protect the club's history. It was not a black-and-white situation, according to McCoist.

"All the conversations I've had with Bill have been positive and he's asked the right questions," said the manager. "I can understand the fans' questions, they are well within their rights to have concerns about anybody. But I would ask the fans to give a chance to whoever gets preferred bidder status."

If only their off-field issues could be dealt with the dismissive ease that United were. Rangers' existence has become an endless endurance test but one thing they didn't have to worry about was winning their penultimate home game of the season. After 20 minutes it was done. Sone Aluko had deposited the ball in the back of Dusan Pernis's net twice by then and Steven Whittaker had scored the first after six minutes.

Aluko has been a rare gem in Rangers' season. His breezy play menaced United although Peter Houston's players conspired enormously in their own downfall. When Jamie Ness played a pass upfield it should have been cleared by Garry Kenneth. Instead he somehow allowed Salim Kerkar to play a through ball for Aluko, who raced away to bury a finish.

Kenneth was implicated again when Aluko scored his second only three minutes later, this time because he allowed the Rangers man to burst between him and Scott Robertson before tucking a low shot past Pernis. Kenneth was hooked at half-time. Whittaker, Kerkar and Lee Wallace all had chances to send United a handful of goals down before the interval.

It was a Rangers team without Steven Davis, Steven Naismith, Kyle Lafferty and Sasa Papac, of course, while from the side well beaten by Celtic at the weekend Lee McCulloch dropped to the bench an injury ruled out Andrew Little altogether. McCoist copied the team he lost to at Parkhead by playing three central defenders although Carlos Bocanegra, Dorin Goian and Kyle Bartley coasted. Jon Daly has been an excellent presence for United all season long but, starved of ammunition, he made no impact. Whittaker and Wallace were the wing-backs and Rhys McCabe and Maurice Edu filled the centre although it was Ness's assured play which caught the eye. Aluko, who might have had a hat trick, played up with Kerkar.

United were a mess. This game should have mattered to them, not Rangers, yet the result and their performance mocked the notion of them finishing third and entering the Champions League qualifiers in July. Yes, they missed the injured Gavin Gunning, yet all the qualities which had them hunting down Motherwell over recent weeks were betrayed by horrendous defending. They had come to Ibrox and dumped Rangers out of the Scottish Cup in February – and beaten them at Tannadice the following month – but this was a different story. Their tackling and marking was poor and they looked jittery and unsure of themselves under Rangers' bombardment. Their dream ended with a whimper. Peter Houston, the United manager, congratulated Motherwell and said: "When we lost 7-1 here we played better that night than we did tonight."

Pernis allowed Whittaker to score the opener by letting his accurate but soft shot squirt into the far corner. Sean Dillon was the guilty man at the fourth when – even after the reprieve of not conceding a penalty when he kicked the ball on to his own hand – he could not clear before the ball reached Ness. The midfielder enhanced a fine performance with a tidy finish to score, and deserved the warm applause which came his way when he was substituted after an hour. Maurice Edu played a ball down the centre of the United half to pick out Alejandro Bedoya, who got the fifth.

"They gave everyone a real tonic after the disappointment of the weekend," said McCoist. "It was a great performance from players who at the start of the season you maybe would not have seen playing in a Rangers jersey."

Would it all have been different if Kenneth's second-minute free kick had not been well saved by Allan McGregor? Or if the goalkeeper hadn't reacted to keep out a Gary Mackay-Steven effort which could have given them an early equaliser? Nope. Their defending was far too careless.

They folded so badly that Rangers, in the 10th match they've played in the shadow of administration, could run up their biggest win of the season.