Motherwell defeated Celtic 2-0 at Fir Park on Tuesday night thanks to goals in either half from Ibrahim Said and Elliot Watt.
Thelo Aasgaard opened the scoring as Rangers closed the gap on leaders Heart of Midlothian to six points with a 2-1 victory over St Mirren at Ibrox.
Hibernian got the better of Aberdeen, winning 2-0 at Easter Road thanks to second-half goals from Thibault Klidje and Junior Hoilett.
Dundee United saw off bottom club Livingston 3-1 in West Lothian to climb into the top six in the William Hill Premiership table.
Charlie Reilly grabbed the winner as Dundee came from behind to earn a crucial 2-1 triumph against Kilmarnock at Dens Park.