Besiktas head coach Senol Gunes on Friday left the Turkish football club, a day after home loss in their European campaign.
Besiktas in a statement said Gunes, 71, met the club's chair Ahmet Nur Cebi after losing to Lugano, told him a change was needed, and would respect every decision by the board.
The Turkish club confirmed Gunes resigned, and thanked him for the efforts and service.
Swiss team Lugano defeated 10-man Besiktas 3-2 in Thursday's third-tier UEFA Europa Conference League group match in Istanbul.
Besiktas forward Vincent Aboubakar scored double before the clock hit 60 minutes. Lugano scored three goals-including an own goal by Eric Bailly-in the final nine minutes to shock the Black Eagles at the Besiktas Park.
Gunes was Besiktas' boss in two different spells, guiding the Istanbul club to back-to-back Turkish Super Lig titles in 2016 and 2017.
His second spell at Besiktas lasted for almost a year.
In the ongoing Super Lig season, Besiktas are ranked fourth spot with 13 points in seven matches, eight points behind leaders and archrivals Fenerbahce.
Gunes' biggest achievement was Türkiye's bronze medal at the 2002 FIFA World Cup co-hosted by South Korea and Japan.
He also coached Turkish Super Lig club Trabzonspor, and won the Turkish Cup.
