Rangers blew the chance to go top of the SPL as Dundee United claimed a last-gasp 3-2 win at Ibrox, while St Mirren recovered to beat Hamilton.
But Rangers were twice pegged back when goals from Nikica Jelavic and Steven Naismith were cancelled out by David Robertson and Johnny Russell before David Goodwillie netted a last-minute winner.
St Mirren striker Michael Higdon's hat-trick all but consigned Hamilton to relegation as they were beaten 3-1.
David Buchanan's drive just before the break gave bottom side Accies the interval lead but in a remarkable 10-minute turnaround Higdon scored with a header, a penalty and a wonderful volley.
Hamilton, who had defender Martin Canning sent off when he conceded the spot-kick with a challenge on Buddies substitute Craig Dargo, are nine points behind the 11th-placed Paisley side and have played a game more.
Chris Humphrey inspired Motherwell to their second victory over Aberdeen since former manager Craig Brown's departure for Pittodrie as the Lanarkshire side opened up a four-point cushion in the race for a top-six place.
Humphrey blasted home inside 15 minutes and set up several more chances before Shaun Hutchinson looked to have made the points safe in the 87th minute.
Nikola Vujadinovic headed Aberdeen back into it in injury time but Motherwell held on to move nine points above the Dons.
St Johnstone were left to rue passing up a host of chances as Kenny Shiels got his caretaker spell in charge of Kilmarnock under way with a goalless draw.
Saints dominated possession and goalmouth opportunities throughout, coming closest when striker Peter MacDonald struck the bar with a second-half header.
MacDonald also had a penalty claim waved away after tangling with Kilmarnock goalkeeper Anssi Jaakkola.
However, a combination of wayward finishing and a string of saves from Jaakkola kept the home side at bay to hand Shiels a point in his first game in charge since Mixu Paatelainen's move to the Finnish national job.
