The 18-year-old striker replaced Pawel Brozek in the 59th minute and volleyed in a Victor Wanyama cross three minutes later from a tight angle, before driving low past Well keeper Darren Randolph from the edge of the box.
Hoops wing-back Cha Du-ri headed in a third to deal a dent to the home side's Champions League aspirations, the Steelmen now only three points ahead of fourth-placed Dundee United having played the same amount of games.
Source: PA
Source: PA