Besiktas suffered a blow to their title hopes after losing 2-1 against Kasimpasa at the Recep Tayyip Erdoğan stadium.
The Black Eagles would have moved six points clear of second placed Fenerbahce with a win but ended the week just three points ahead having played an additional game over their Istanbul rivals.
Besiktas took an early lead on 28 minutes when Oguzhan Ozyakup setup Jose Sosa with a defence splitting pass allowing the Argentinian in on goal before finding the back of the net with a cheeky dink over the keeper.
Kasimpasa replied just a minute later when Del Valle eased passed Beck before beating Boyko at his near post.
Besiktas boss Senol Gunes brought on Tolgay Arslan for Kerim Frei in the second half but the move backfired. Frei pushed forward in the first half and forced the Kasimpasa full-back to stay in a defensive position.
The home side flooded forwards after Frei was taken off and while Arslan was in theory supposed to sure up the midfield he was clearly not ready after a long spell on the sidelines.
Scarione exploited more shoddy Besiktas defending to give his side the lead and to be fair Kasimpasa could easily have scored again had Koita not been so wasteful.
KASIMPAŞA 2-1 BEŞİKTAŞ
Stadium: Recep Tayyip Erdoğan
Referee: Mete Kalkavan
Kasimpasa Köse, Popov, Omeruo, Titi, Veigneau, Hakan Arslan, Adem Büyük (min. 79 Tunay Torun), Castro, Scarione (min. 84 Abdullah Durak), Del Valle (min. 75 Koita), Eren Derdiyok
Manager: Rıza Çalımbay
Besiktas: Boyko, Beck, Marcelo, Necip Uysal, İsmail Köybaşı, Hutchinson (min. 90 Mustafa Pektemek), Oğuzhan Özyakup, Kerim Frei (min. 46 Tolgay Arslan), Sosa, Olcay Şahan (min. 57 Cenk Tosun), Gomez
Manager: Şenol Güneş
Goals: min. 28 Sosa (Beşiktaş), min. 29 Del Valle, min. 49 Scarione (Kasımpaşa)
Yellow Cards: min. 17 Hakan Arslan (Kasımpaşa), min. 45+1 Oğuzhan Özyakup, min. 54 Marcelo, min. 90+5 Sosa (Beşiktaş)