The game was drifting aimlessly before the 18-year-old came on just shy of the hour mark but he soon turned the tide with two goals within three minutes.

Watt expertly volleyed in Victor Wanyama's cross on 63 minutes, just after replacing Pawel Brozek, and drove past Motherwell goalkeeper Darren Randolph from the edge of the box for his second.

Wing-back Cha Du-ri headed in a third seven minutes from time as Motherwell's Champions League aspirations took a huge hit.

They are now 11 points behind Rangers in third with Celtic well ahead in first place by 18 points.

A Dean Shiels penalty just prior to half-time helped Kilmarnock to a 1-0 win away at Hibernian.

Team-mate Liam Kelly then missed a chance from the spot to double their advantage five minutes after the break, but it mattered little to the contest at Easter Road Stadium.