In the 50th minute, Koopmeiners decided to try from a distance and his shot from about 25 meters surprised goalkeeper Lorenzo Montipò, who still touched the ball. For 24-year-old Koopmeiners, who scored four goals last season, it was his first goal of the season.
Koopmeiners got the ball passed by Marten de Roon, who, like the match winner, played the entire match. Hans Hateboer was sidelined halfway through the second half by trainer Gian Piero Gasperini.
Napoli not past Fiorentina
Napoli also failed to win the third game in Serie A. In the away match against Fiorentina, the team of coach Luciano Spalletti did not go further than 0-0.
Napoli, which was linked to Ajax earlier this week in the group stage of the Champions League, could have become the only club with 9 points after three matches. AC Milan, Lazio, Atalanta, Torino and AS Roma are also on 7 points.
Fiorentina also played a goalless draw against FC Twente in Enschede on Thursday, in the play-offs of the Conference League. Because Twente was defeated 2-1 in Florence, Fiorentina qualified for the group stage.
Salernitana was much too strong for Sampdoria at home with 4-0. Former Feyenoord player Tonny Vilhena, who came over from Espanyol this summer, scored the third goal.