McDonald and Diamond both scored for the Dons at Pittodrie
Two Zander Diamond goals within three second-half minutes secured Aberdeen a thrilling victory over Scottish Premier League leaders Celtic at Pittodrie.
Gary McDonald looped in a header to give the Dons the lead after 24 minutes, but Scott Brown fired an equaliser within a minute.
Stuart Duff's half-volley put the Dons back in front, only for Scott McDonald to reply with a second-half header.
But defender Diamond scored twice from close range to secure a Dons win.
It was Aberdeen's sixth consecutive victory at Pittodrie and moved them into third in the SPL ahead of Dundee United, who were already 3-0 down at home to Motherwell down the A90 at Tannadice.
And it meant that Celtic failed to extend their lead at the top, Rangers having reduced the gap to two points with their win over Falkirk on Saturday.
Celtic had suffered a blow even before kick-off, with a groin injury picked up during the warm-up forcing Poland international goalkeeper Artur Boruc to miss the game.
Mark Brown came into the starting line-up - the sixth change to the Celtic side that beat Dundee in the Scottish Cup - but it meant they did not have a substitute keeper on the bench.
Yet it was the visitors who started the brighter against a nervous-looking Aberdeen.
Georgios Samaras was denied twice, once by a goal-line clearance by Richard Foster and a point-blank stop by goalkeeper Jamie Langfield as the Greek tried to stab home from close range.
But Aberdeen began to work their way into the game and they claimed for a penalty when Scott Brown nipped in to prevent the ball reaching Gary McDonald on the edge of the six-yard box.
Brown made it 1-1 a minute after Aberdeen had taken the lead
The home side made the breakthrough after 24 minutes when Duff, who had returned to the Dons starting line-up in place of Andrew Considine, found McDonald with his cross and the midfielder looped a header into the far corner of the net from 12 yards.
Celtic hit back within a minute when Aiden McGeady sped past Foster and, when his low cross was dummied by Scott McDonald, Brown side-footed home from just inside the penalty box.
Another six minutes, another goal. Mark Kerr found Duff in space with a fine ball over the Celtic defence and the midfielder's drive zipped low past Brown from 16 yards.
Celtic pressed forward in search of another equaliser, but it was Aberdeen who went closest to adding to the scoreline before the break.
Lee Miller looped the ball over Brown from an acute angle within the six-yard box, but Gary Caldwell hooked it clear before it could cross the goal-line.
Celtic forced Aberdeen onto the back foot after the break and the reigning champions were unfortunate not to take the lead on the hour mark.
Andreas Hinkel's cross deceived Langfield, came back off the inside of the far post and Paul Hartley blasted the rebound over from 15 yards.
And Celtic's incessant pressure paid off after 73 minutes when Scott McDonald rose to head home Barry Robson's outswinging cross from 10 yards.
But Aberdeen hit back with two Diamond goals within the next five minutes - both from curling free-kicks to the back post from Charlie Mulgrew.
First, the central defender dived to head home with Celtic making strong claims that referee Dougie McDonald had already been blown for a foul.
Then he stretched a long leg to force the ball home off the despairing hand of goalkeeper Brown.
Aberdeen manager Jimmy Calderwood: "It was a fabulous advertisement for Scottish football and it is a massive boost for us to beat the champions.
"We took a lot of flak round about September/October when we were bottom of the league.
"But we've got the youngest team in the SPL with a lot of new boys and, all credit to them, they have done wonderfully well to turn it around.
"I thought we deserved to win the game, we are now in third and there's no reason why we can't keep the momentum going."
Celtic manager Gordon Strachan: "The consolation is that my team played well, made chances, showed great determination and great character, while the two goals we scored were absolutely fantastic.
"If they play like that for the rest of the season, I will be happy. If they defend like that at set-plays, I will be a worried man.
"The thing that let us down is that they scored four goals from four free-kicks and we have to see if there is a common denominator there and eradicate it.
"I feel sorry for Mark Brown, because he has not had a save to make and has not been able to show his ability."
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