In the CRM application when I create a new Account record the Owner is defaulted to me. When I create a new Opportunity I have to look up my name to make me the owner.
Try this:
"Object view" page> Lookup field edit > Check box "By default attach the current user to newly created Opportunity"
Yes, edit the page the lookup field appears on, select the lookup field, and in the properties box, make sure the checkbox called "By default attach the current user to newly created Opportunity" is checked. Save your page.