ABERDEEN suffered a 10th straight defeat to Celtic as they lost 2-0 at Pittodrie to fall 12 points behind the league leaders.
Both sides were reduced to 10 men as Mikael Lustig received a second yellow for the Hoops in the second half.
January signing Sam Cosgrove was then sent off with a straight red for a lunge on Scott Brown – just eight minutes after coming on for his Dons debut after joining from Carlisle.
It was a second straight defeat for the Reds following a 2-0 loss at Hibs last weekend.
Aberdeen have lost further ground on second placed Rangers and trail the Ibrox club by three points.
There were two changes to the side that lost 2-0 to Hibs at Easter Road with one enforced.
On loan Celtic play-maker Ryan Christie was ineligible as he cannot face his parent club due to the terms of his loan agreement.
Icelandic international defender Kari Arnason returned to the starting line-up.
Striker Stevie May came in for his first start since the 4-1 defeat of Hibs in mid December having recovered from an ankle injury.
The £400,000 summer signing was introduced as a second half substitute at Hibs last weekend to complete his comeback with Adam Rooney dropping to the bench.
Influential skipper Graeme Shinnie was also out, serving the last of a two game suspension.
Aberdeen came close to grabbing the lead in the sixth minute when a free kick was awarded for a foul by Jozo Simunovic on May.
From the right Kenny McLean curled in a superb delivery along the face of goal and Kari Arnason just needed to touch it to net at the back post but it flew wide.
It illustrated the vulnerability of that central defensive area with Celtic.
In the 14th minute the Reds again threatened when a long throw in from Arnason on the right was deflected towards O’Connor just a few yards from goal but he couldn’t make the proper contact.
Celtic should have taken the lead in the 19th minute when Scott Sinclair burst down the left pat Shaleum Logan and found Moussa Dembele with a measured pass.
The striker checked and changed feet and the momentum was lost. The ball then fell to Tom Rogic whose drive was blocked by on loan Newcastle United keeper Freddie Woodman.
Moments later Nwakali blasted a volley on the half turn well over from 30 yards.
McLean displayed superb vision to flight a cross in behind the defence in the 26th minute. May reacted with a perfectly timed run to breach the rear-guard and was unfortunate not to connect at the back post.
Aberdeen were threatening and growing in confidence.
On the half hour mark Niall McGinn delivered a corner from the left that O’Connor met at the near post but his glancing eight yard header was straight at keeper Dorus de Vries.
Soon after keeper Woodman raced out to charge down Rogic and block his header at the edge of the box.
The woodwork denied Celtic in the 35th minute when Olivier Ntcham’s drive crashed off the post as he curled it around the Dons defence.
It was an ominous sign as Celtic went ahead in the 37th minute when James Forrest got past Andy Considine on the left and dinked a dangerous cross to the back post.
DEMBELE charged in at the back post after losing his marker Arnason to power home a close range header.
Early in the second half Scott McKenna connected with a Mackay-Steven corner but his 18 yard header went over.
Aberdeen should have levrelled on the hour mark when Kristoffer Ajer and Mikael Lustig collided. The loose ball fell to O’Connor who passed it left to Mackay-Steven.
The winger raced in on goal with the defence struggling and rather than taking on a shot he opted to slide a pass to the onrushing May but he failed to connect. It was a missed chance.
The collision between Ajer and Lustig underlined the lack of communication in that back-line.
Aberdeen were more in the faces of Celtic in the second half and were showing more appetite for the clash.
There was a three pronged chance when Kenny McLean’s shot was blocked by de Vries. McGinn then pounced on the loose ball but his shot was cleared off the line and then O’Connor’s effort was charged down.
In the 75th minute Lustig was sent off for a second yellow for a wild challenge on Mackay-Steven.
10 man Celtic wrapped up the points in the 83rd minute when Dembele drove forward and released a perfect pass to Kieran TIERNEY who unleashed a vicious left footed shot from the left side of the box to the bottom right corner.
It was a lethal counter attack.
To deepen the Dons’ agony January signing Sam Cosgrove was red carded when he lunged in on Scott Brown in a foolish challenge on his first team debut.- just eight minutes after coming on.
ABERDEEN: Woodman, Logan, Considine, O’Connor, McLean, Mackay-Steven, Arnason, McGinn, McKenna, Nwakali, May.
Subs: Cosgrove (for May 76), Rooney (for Nwakali 82), Maynard (for Arnason 90)
Subs not used: Rogers, Reynolds, Rooney, Wright, Ball.
CELTIC: De Vries, Lustig, Simunovic, Ajer, Tierney, Forrest, Brown, Ntcham, Rogic, Sinclair, Dembele.
Subs: McGregor (for Rogic 72), Hendry (for Forrest 78), Edouard (for Sinclair 81)
Subs not used: Bain, Hendry, Miller, Kouassi, Musonda.
Referee: Bobby Madden