New Aberdeen manager Stephen Glass and Aberdeen suffered bitter heartache as a last-gasp equaliser denied them a vital win against Celtic.
The Reds were on course for a huge victory until Leigh Griffiths scored late into injury time.
It was a hammer blow for Aberdeen to hopes of leapfrogging Hibs into third this sesaon.
It was devastating for a Dons side which had put so much into the game and were so close to delivering a win for Glass in his first Premiership game in charge.
After Hibs had defeated Livingston 2-1 in an earlier kick-off, this was a game Aberdeen had to win.
Aberdeen had grabbed the lead through Lewis Ferguso,n but Griffiths netted late on.
Both sides also hit the woodwork through Ferguson and Celtic’s David Turnbull.
However, Aberdeen suffered an injury blow with Ross McCrorie taken off after just 14 minutes with an injury.
There were three changes to the Aberdeen starting XI that edged out Livingston 5-3 in a penalty shoot-out in the Scottish Cup fourth round on Saturday.
One was enforced with keeper and captain Joe Lewis ruled out with a rib injury suffered in the cup tie.
Although X-rays confirmed no broken ribs, Lewis was in too much pain to face Celtic and sat out with on-loan Oldham Athletic Gary Woods coming in for his first start.
Woods came on for Lewis in the first half of the cup tie against Livingston.
On-loan St Gallen striker Florian Kamberi came into the starting line-up having impressed coming in off the left in the cup tie, where he netted his first Dons goal.
St Johnstone loan striker Callum Hendry also started.
Dropping to the bench were Connor McLennan and on-loan Stade de Reims striker Fraser Hornby.
Celtic skipper Scott Brown was pitched in from the start against his future Aberdeen team-mates.
Midfielder Brown, 35, rejected the offer of a new Celtic contract in favour of moving to Aberdeen in the summer.
He will join the Dons on a two-year deal in a player-coach role.
Not because he is set to be a Dons player, but because Glass believes he remains so important and key to Celtic.
Aberdeen created the first opportunity in the third minute when Matty Kennedy found Lewis Ferguson with a cross and the midfielder’s looping 15-yard header produced a strong save from keeper Scott Bain.
The loose ball fell to Callum Hendry, but his low drive at the near post was turned behind by Jonjoe Kenny.
In the 12th minute, keeper Woods dived to block a David Turnbull free-kick fired in from 22 yards.
Aberdeen suffered an injury blow when McCrorie had to come off with an injury suffered in a collision with Odsonne Edouard.
After treatment, he carried on for two minutes but then sank to the pitch and had to come off.
He was replaced by 17-year-old right-back Calvin Ramsay.
Aberdeen went ahead in the 18th minute when Andy Considine met an inswinging corner from McGinn.
He powered in a header and FERGUSON was on hand to direct it over the line.
It was Ferguson’s 10th goal of the season and his first since netting a brace of penalties in a 3-3 draw with Celtic in October.
Ferguson nearly netted moments later when he was allowed a free header from another corner, but Bain got down to save at his near post.
Keeper Woods produced a vital block when Odsonne Edouard was left unmarked eight yards out, but his shot was straight at the stopper, who reacted sharply.
Again the Reds threatened when Ferguson fired in a dangerous effort from 15 yards that forced a save from Bain.
Moments later the Reds again had Celtic on the back-foot when Niall McGinn smashed a left-footed strike into the side netting from the edge of the box.
Celtic were ripped apart at the back.
Aberdeen were fired up.
Celtic were denied in the 39th minute when Woods saved from Edouard with Christie firing in the rebound that was blocked and put wide by Hayes.
From the corner kick, a flicked Christie header beat Woods, but Ferguson produced a superb diving header to clear off the line and put the effort over the bar.
Moments later Edouard finally had the ball in the Aberdeen net, but the Celtic striker was ruled offside.
Half-time: Aberdeen 1 Celtic 0
The woodwork denied Celtic in the 52nd minute when Edouard found Turnbull with a knock-down.
Turnbull unleashed a powerful effort with the outside of his right boot that beat Woods, but cracked off he cross-bar.
Celtic were looking increasingly dangerous on the attack.
It should have been 2-0 in the 65th minute when Brown got back to intercept a pass from Hendry only to redirect the ball into the path of Ferguson, who was wide open.
With the goal beckoning, Ferguson rattled the right hand post.
He should have scored. It was a glorious chance.
Moments later, Turnbull fired a drive along the face of goal.
Aberdeen hit on the break when Hayes burst up field from his own box and was charged down by McGregor.
As he broke into the Celtic box both McGregor and the onrushing Bain closed him down and the chance was gone.
Hayes called for a penalty, but referee Willie Collum waved play on.
Aberdeen suffered devastating heartache in time added on when Elyounnoussi crossed to substitute GRIFFITHS who headed beyond Woods.
The Dons then kicked off and Collum immediately blew for full-time.
Full-time: Aberdeen 1 Celtic 1
ABERDEEN: Gary Woods, Tommie Hoban, Andy Considine, Callum Hendry, Niall McGinn, Jonny Hayes, Lewis Ferguson, Florian Kamberi, Dean Campbell, Matty Kennedy, Ross McCrorie.
Subs: Calvin Ramsay (for McCrorie 14), Dylan McGeouch (for McGinn 66), Jack MacKenzie (for Hendry 66).
Subs not used: Tom Ritchie, Fraser Hornby, Connor McLennan, Ethan Ross, Michael Ruth, Ryan Duncan.
CELTIC: Scott Bain, Greg Taylor, Nir Biton, Scott Brown, David Turnbull, Jonjoe Kenny, Ryan Christie, Odsonne Edouard, Mohamed Elyounoussi, Callum McGregor, Stephen Welsh.
Subs: Tom Rogic (for Christie 60), Leigh Griffiths (for Edouard 60), Karamoko Dembele (for Brown 80).
Subs not used: Conor Hazard, Ismaila Soro, Dane Murray, Adam Montgomery, Anthony Ralston, Diego Laxalt.
Referee: William Collum