The English-born forward, who qualifies to play for Northern Ireland through his grandmother, scored the winner in a 1-0 victory over Slovenia at Windsor Park on his first ever visit to the country on Monday.
The 23-year-old, who signed for QPR from Peterborough United for around £2.5 million in the January transfer window, was making just his second appearance for Michael O'Neill's side having made his debut against Wales just four days earlier.
Washington said: "It was crazy to be fair. I had the chance earlier and I was a little bit disappointed not to see that one go in. The ball has come over the top and I just tried to move [the defender] out of the way. I managed to and then move the second guy and cut inside, and I think the keeper was already going far corner so I thought I’d try and stick it in the near corner and it paid off.
"It's been an unbelievable four years but this last 6-8 months have been a bit of a fairytale. I am pleased to get another start and a goal but I have got to keep working hard towards the end of the season with QPR and see where that takes me.
"They [his international teammates] have made it so easy for me to come in, so welcoming. All the lads are brilliant with no egos here and I think that is why they’ve been so successful. I’ve really enjoyed my week."
Washington will now have his sights set on ensuring he is on the plane to France for Euro 2016 this summer as Northern Ireland prepare for their first major tournament in 30 years.
In order to secure his place he will be desperate to start scoring at club level again, having failed to find the net in any of his eight appearances for QPR since his move after hitting 15 in 31 games for Peterborough earlier this season.