With play heavily focused in the middle of the pitch, Washington's goal from a counter attack proved the difference.

The QPR striker outmuscled two Slovenian defenders before creating room in the box to blast a low shot past goalkeeper Jan Oblak.

Slovenia created few chances on the Northern Ireland goal, but should have equalised in the 66th penalty when Mirel Samadržić was brought down in the box to earn a penalty.

Veteran striker Milivoje Novaković's effort from 11 metres was saved by goalkeeper Roy Carroll.

Opening a series of friendlies ahead of the start of qualifying for the 2018 World Cup, Slovenia have one win and one loss.

They will play the next friendly against Sweden in Malmo on 30 May.