I. up ‧ stage 1 /ʌpˈsteɪdʒ/ BrE AmE verb [transitive]
to do something that takes people’s attention away from someone else who is more important:
All the big-name stars were upstaged by 12-year-old Katy Rochford.
II. upstage 2 BrE AmE adverb
towards the back of the stage in a theatre OPP downstage
—upstage adjective