It was Newcastle goalkeeper Krul who had to watch on helplessly as Pieters' attempted cross from the left drifted over his head and dropped inside the far post.
Pieters and Krul have been friends since playing together for the Dutch Under-17 team, and the full-back joked: "I told him I meant it.
"Everybody knows he's my best friend in football. I've known him since I was 17. It was really good to score my first goal, and a great goal as well, against him.
"We talk to each other a lot, about our personal lives as well. We support each other always and we have a good relationship. I'll keep texting him, for sure."