Johnson grew up at the Hammers and refused to celebrate after he opened the scoring with a belter in the 3-2 win.
He said: "I knew from the beginning that if I scored I was not going to celebrate. I spent the longest part of my young career here, I've got a lot of love for the club and the fans so I try not to celebrate.
"It was a nice strike I got behind it well. As soon as I hit it, I thought this has got a chance. Any other ground and I would have gone crazy."