The Turkish striker broke the deadlock in the 75th minute when Croatian keeper Danijel Subasic could only push a shot from Oguzhan Ozyakup away towards the feet of Tosun who fired the ball into the net.
Turkey's prospects had been dented on Saturday when they lost 2-0 to Ukraine but they are back in contention after the win in front of a raucous home crowd in the northwestern Turkish city of Eskisehir.
Chances fell to both teams in an attacking opening spell, with Croatia almost scoring from a Luka Modric free kick in the 10th minute that ricocheted of Burak Yilmaz's shoulder and onto the post as he tried to clear.
A minute later Turkey had a good opportunity to take the lead when Arda Turan crossed to Tosun, but he fired the ball wide from close range.
The second half started in a similar attacking fashion, with a Modric free kick setting up Dejan Lovren, who could only head the ball straight at Turkish keeper Volkan Babacan.
A few minutes of sustained Turkish pressure then followed but both Kaan Ayhan and Burak Yilmaz fired wide.
Tosun's goal took Turkey up to 14 points in Group I after eight games, level with Ukraine on points and trailing Croatia and Iceland who both have 16 points after the latter beat Ukraine.
(Writing by Daren Butler,; Editing by Jeremy Gaunt and Toby Davis)
