How do you do it?

you do the thing with the thing and then the thing happens

True enough

For future players who come see this thread. The trick works by leaving the first enemy alone > Killing everyone else > walking to where Tony will be > then luring and killing the first enemy. This only works if you lure and kill the first guy. No one else works.

You can kill a last guy, but if you play on Corey. Like this: