Hearts rang the changes after their 5-0 defeat to Livingston, with five players coming into the starting XI, but goalkeeper Colin Doyle would not have been happy with his first touch.

That was to pick the ball out of the net after Stevie May's cross from the left found Cosgrove at the back post, and he rose to power a header past the Irish goalkeeper and into the top-right corner of the net.

The ball was in Hearts' net again after 24 minutes as Doyle completely missed Shay Logan's swept cross, but Lewis Ferguson was penalised for a foul on the goalkeeper and the free-kick was given.

Hearts' best effort of the first half came just after the half hour when a cleverly-worked free-kick between Olly Lee and Oliver Bozanic created an opening for Steven MacLean, but Joe Lewis blocked the former St Johnstone striker's effort.

But Doyle was struggling at the other end and a panicked clearance just before the interval gave Aberdeen the opportunity to take a quick throw-in, but Graeme Shinnie's effort was well off-target.

The Dons were dealt a blow moments after the break when Max Lowe, the on-loan Derby left back who is set to return to his parent club in January, pulled up with a groin injury that will surely make this his last appearance for the Pittodrie club.

That seemed to knock Aberdeen out their stride but for all their possession, Hearts failed to create a clear-cut chance.

And they were punished for that failing, midway through the second half as Cosgrove rolled home his second from the penalty spot after Christophe Berra had hauled down his fellow Scotland international centre-back Scott McKenna.

The points were safe, but Hearts' cause was not helped by the sending off of Mitchell. The on-loan Manchester United man had been booked for a foul on Connor McLennan, and with four minutes left saw a second yellow bringing down Dean Campbell.

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