Originally Posted by
goodeats21
If this is all on the same ticket, you should be able to enter the SFO PL, and your SFO-LAS BP should provide the access. Obviously, hang onto your LHR->EWR boarding pass in case they ask to see it.
If you do this report back and let us know what happens in SFO. You could get green and go in normally or red and they ask to see your boarding pass.