How to make Opportunity records private for Sales Manager role?

Hello,

I want to make Opportunity record visible only to the respective owner (for Sales Manger role) of the records. I have changed default setting to User, see image below:

But it doesn't seems working, I have two users with Sales Manger role, UserA and UserB. 

I have created record using UserA's account but it still visible to UserB.

Anything am I missing?

Regards,

Ashish