Two quick-fire Zander Diamond goals earned Aberdeen a memorable 4-2 win over Celtic at Pittodrie, while Motherwell thumped Dundee United at Tannadice.
The home side broke the deadlock on 24 minutes when Gary McDonald headed home Stuart Duff's cross, but the lead proved short-lived as Scott Brown drew Celtic level a minute later after some fine approach work by Aiden McGeady.
Aberdeen restored their lead just past the half-hour mark with a fine volleyed finish from Duff.
Celtic threw everything at Aberdeen in the second half and they drew level on 73 minutes when Scott McDonald headed home Barry Robson's precise cross.
However, Aberdeen refused to lie down and grabbed the lead for a third time 15 minutes from time when Diamond got on the end of Charlie Mulgrew's inviting free-kick to head home past Mark Brown. There was some confusion over the goal with the referee Dougie McDonald blowing for an offence in the box before allowing the goal.
Diamond finished off Celtic three minutes later when he bundled the ball home from close-range after the visiting defence failed to deal with another Mulgrew delivery into the box.
The defeat means Gordon Strachan's side sit just two points clear of Rangers at the top of the table, while Aberdeen are eyeing a place in Europe.
Motherwell moved up to seventh spot in the table with a stunning 4-0 win over Dundee United.
Marc Fitzpatrick set Mark McGhee's men on their way with a fine headed opener on 23 minutes and Maros Klimpl doubled the lead four minutes later with his first goal for the club.
David Clarkson added a third for Motherwell on 33 minutes with a clinical finish to leave United facing an uphill battle.
Motherwell completed the rout on 63 minutes when Chris Porter got his name on the scoresheet to seal a resounding victory for the visitors.