Jordan Zemura struck a superb free-kick 15 minutes from time to earn the triumph.
Runjaic said afterwards: "It was an important match, it was important to give a response and find the three points in front of our fans. We showed that we can be an uncomfortable team for everyone, but in the first half I didn't like some things, we were slow in moving the ball and we could have even gone behind. After that we grew.
"We have been working for three months, I think we have gotten to know each other well in these months, we always learn something new every week. Normally it is the players who win the games, not the coaches, we try to do our best during the week and in the game we try to make an impact with the substitutions, sometimes it goes well other times not.
"During the break I saw the boys very self-critical about how they had played in the first half, continuing like that we could have lost in the second half. On the substitutions I also thought about Rui Modesto, but he has just arrived and I made a different decision by making a different type of substitution.
"Zemura is a very good player with both feet, the move worked and I am happy, he is a boy who has potential to be exploited further."