On-loan Chelsea defender Kenneth Omeruo started for Kasimpasa after an injury that ruled him out of international football for Nigerian last week.
The young defender shared an Instagram post after the game expressing his delight at beating the league leaders.
Omeruo dealt with Besiktas’ aerial threat winning all his duals in the air and making the highest number of clearances for his side (7).
The Black Eagles struggled to find a way past the 21-year-old who put on a solid defensive display for Kasimpasa.
Omeruo has now made 20 appearances since joining the Istanbul minnows on loan from Chelsea over the summer.
The Istanbul based side have a release clause option but Chelsea may be reluctant to sell considering the kind of form he has been in this season.
The victory moved Kasimpasa into 7th place just four points off fourth placed Basaksehir. Besiktas meanwhile remained in first place despite their defeat three points clear of second placed Fenerbahce.