Isak struck the winner as Newcastle defeated Spurs 2-1.
He said, "It is my first goal for the season so it's a good feeling that I score that one and we get the win.
"Generally we weren't expecting to have too much of the ball. We wanted to be dangerous on the counter-attack. It wasn't the most beautiful game from our side but we defended really well and scored two so that's good.
"You always have to be concentrated. It's easy to get frustrated. It was a tough game and tough for me - I wasn't at my sharpest. Jacob Murphy had a great assist, very selfless, so it was just being in the right place.
"We've always, at home, felt like we have that extra energy. We have spoken about using that. In the second half when we had a bit of a dip in our performance, we got some energy. Small changes made a big difference and really helped us get the win."