There was nowhere online (albeit I only performed a quick Google search) that I could find saying how to make Safari’s search open in a new tab, so here’s how to do it:
The shortcut to get the the search box is Command + Option + F
Type in your query and then press Command + Return and boom! Search in a new tab.
Another tweak I like to do is to go into Safari’s Tabs preferences and check “When a new tab or window opens, make it active”.