Steven Gerrard admits Rangers have taken a step back after relinquishing the title race lead after just three days.
The Ibrox side hit the front with Sunday's win over Hearts but they could not back that Tynecastle result up against Aberdeen.
Scott McKenna fired the only goal of the game as Gerrard suffered his first home defeat of his Gers reign.
Both teams finished with 10 men as Alfredo Morelos followed Dons striker Sam Cosgrove down the tunnel.
— Rangers Football Club (@RangersFC) December 5, 2018
But Gerrard had more than just his side's latest red card to be frustrated about.
He said: "I'm very disappointed in our performance. Very frustrated in the performance.
"Tonight was a really good opportunity and a difficult test for us – but one that I had confidence that we could pass. Unfortunately we've failed.
"The performance as a group wasn't good enough to beat Aberdeen, even at 11 v 10 the performance wasn't good enough.
"We've got the majority of things wrong tonight all over the pitch.
"I never felt once today good about anything that we did, individually or collectively. I never felt good.
"I give the players so much praise and they have done extremely well before this game, we were in a really good place.
"But today is certainly a big set-back and a frustrating one."
McKenna crashed home a left-foot volley after seven minutes, but Aberdeen had to battle on for the final hour a man down after Cosgrove was given a second yellow following a collision with Jon Flanagan.
Morelos' lack of control saw the numbers evened up when he caught Graeme Shinnie midway through the second half.
Dons boss Derek McInnes admitted victory was the perfect pick-me up for his side as they bounced back from losing Sunday's Betfred Cup final to Celtic.
"We had to pick ourselves off the floor after Sunday but I was pleased with a lot of the aspects of the game," said boss Derek McInnes.
"It's a real shot in the arm when you see the players put so much in. There was tenacity all over the pitch. We got our just rewards."