The Well found themselves 4-1 down at half-time as Jon Obika's brace, either side of Liam Polworth's equaliser, an own goal from Peter Hartley and Sam Foley's strike put the visitors in firm control of the fifth round tie at Fir Park.

However, Tony Watt pulled one back for the hosts before Aarons - who spent the first half of the season at League One outfit Wycombe Wanderers - halved the deficit with the 24-year-old's cross-cum shot catching out Saints goalkeeper Václav Hladky.

Within 60 seconds, Motherwell found themselves level as Allan Campbell completed the spirited comeback as his deflected cross found the net.

With neither side unable to find a winner after 90 minutes as well as extra-time, the game headed into a penalty-shoot-out.

After only one of the first five penalties were converted, Aarons got Motherwell off the mark from the spot before Jermaine Hylton's miss from 12 yards ultimately sent St. Mirren through to the quarter-finals with a 3-2 win.