Kasimpasa pulled off a huge shock after beating rivals Galatasaray 2-1 at the Recep Tayyip Erdoğan stadium in the mini Istanbul derby.
The Lions actually took the lead after Garry Rodrigues opened the scoring 37 minutes.
Kasimpasa equalised just before half-time when Diagne netted a last-gasp penalty.
Koita scored on 80 minutes to give his side a surprise victory.
Chelsea defender Kenneth Omerou started for Kasimpasa and put on yet another impressive display.
Omeruo made three tackles for the Istanbul minnows and the highest number of clearances in the entire game (14).
The Nigeria international has started the last 17 games for the Istanbul minnows.
Omeruo has spent the last three years on loan at Super Lig sides.
The win moved Kasimpasa up into 9th place, Galatasaray meanwhile remained in second position.
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Kasımpaşa 2 – 1 Galatasaray
Stadium: Kasımpaşa Recep Tayyip Erdoğan
Referee: Halis Özkahya, Kemal Yılmaz, Cevdet Kömürcüoğlu
Kasımpaşa: Ramazan Köse, Veysel Sarı, Omeruo, Ben Youssef, Veigneau, Sadiku, Pavelka, Mensah (min. 80 İlhan Depe), Trezeguet (min. 90+4 Ahmed Ildız), Koita, Diagne (min. 71 Eduok)
Galatasaray: Muslera, Linnes, Serdar Aziz (min. 46 Eren Derdiyok), Maicon, Nagatomo, Donk, Tolga Ciğerci, Feghouli (min. 59 Sinan Gümüş), Selçuk İnan (min. 82 Yasin Öztekin), Rodrigues, Gomis
Goals: min. 37 Rodrigues (Galatasaray), min. 45+3 Diagne (Penaltıdan), min. 80 Koita (Kasımpaşa)
Yellow Cards: min. 17 Nagatomo, min. 49 Tolga Ciğerci, min. 79 Rodrigues (Galatasaray), min. 36 Veigneau, min. 55 Sadiku, min. 90+1 İlhan Depe, 90+5 Koita (Kasımpaşa)
