With the strike, the 24-year-old opened his goal account for the Apaches.
Mensah expertly side-footed a curling effort from outside the box after receiving a lay-off from Nigerian attacker Samuel Eduok to open the scoring in the tenth minute.
He came close to doubling the lead moments thereafter after dazzling his way into the box but had his effort wrack the upright.
John Romana restored Kasimpasa’s lead after Castro had drawn Goztepe level in the 47thminute.
Than Mensah’s run from deep in midfield saw him provide an assist for his side’s third goal after he set-up Strahil Popov who finished from a tight angle.
The Accra-born midfielder who is capped four times for the Black Stars is currently on loan to the Istanbul side from Atletico Madrid.
He was also previously on loan to Getafe and Vitoria Guimaraes.