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.
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