Luck shone on the Senegal striker as the ball deflected off his back into the net from a Sammy Ameobi shot deep into stoppage time.
West Brom rallied and for periods continued the fine form they have displayed this season by outplaying their hosts. On-loan Chelsea striker Romelu Lukaku thought he had equalised when he glanced home a Youssuf Mulumbu shot past Tim Krul, only for it to be ruled offside.
On 55 minutes the big Belgian finally got the goal he deserved, powering home a header at the back post after some great work from Zoltan Gera.
The Baggies continued to play some lovely football but it was Alan Pardew's men who grabbed the victory in the closing stages providing heartbreak to the traveling side.
The victory sees Newcastle move into the top half whilst West Brom remain in an impressive eighth place after nine games.
Sports Direct Arena, Newcastle-upon-Tyne – 49,731