Hearts 2 Aberdeen 0
Aberdeen slipped to third in the league after two quickfire first-half goals saw them beaten 2-0 at Hearts.
Strikes from Steven Naismith and David Milinkovic mean the Dons go into the split third in the Scottish Premiership after Rangers beat Dundee.
The pair scored within two minutes of each other to capitalise on some slack defending to open a lead that Aberdeen never looked like closing as the Jambos' unbeaten home run extended to 14 games.
The visitors hit the post twice but were comfortably second best as they slipped below Gers in the table.
It was an even start to the game, with both sides enjoying good chances in the opening minutes before a double salvo put the hosts in charge.
They were almost ahead within five minutes following some slack defending as the Aberdeen defence got caught sleeping under a high ball and Joe Lewis was forced into a poor clearance.
A sloppy touch from Milinkovic robbed him of the chance to shoot with Lewis out of his area, but instead found Kyle Lafferty who curled over from the corner of the area.
Andy Considine glanced a header against the post from a fine Niall McGinn free-kick and Shay Logan hit straight at Jon McLaughlin before the hosts took the lead.
The influential Naismith was the man to break the deadlock after being played in by Milinkovic down the left of the box before cutting in and curling in for his second in as many home games.
Derek McInnes' fury was compounded minutes later as another moment of hesitancy from the defence saw Lafferty pick the ball up from deep and his shot deflected into the path of Milinkovic, who took his time before slotting confidently for a two-goal lead.
Aberdeen, who had dominated possession up to that point, resumed control of the ball but there was little to encourage McInnes in front of goal as they went into the break 2-0 down.
The Dons boss changed their shape but Hearts started the half on top and were rarely troubled in the early exchanges.
The hosts were happy to sit on their two-goal lead, and only threatened the Aberdeen goal when Christophe Berra charged out of defence before firing over the bar from distance.
The introduction of Gary Mackay-Steven from the bench offered glimpses of the visitors as an attacking threat, but the winger saw a low effort easily saved and then dragged another attempt wide when well placed.
Adam Rooney crashed a half-volley against the post in the last 10 minutes as Aberdeen applied late pressure but McLaughlin remained unbeaten as Hearts claimed the win.