Albion's first Saturday home defeat for more than two and a half years was overshadowed by an injury blow for Bobby Zamora.
The Seagulls hotshot hobbled off after 36 minutes with suspected ligament damage.
Zamora was hurt in a tackle with Norwich defender Darren Kenton.
He came back on after treatment, but it immediately came clear that he could not continue.
Youngster Daniel Marney came on for his first League appearance to form a rooky strike force with Shaun Wilkinson, making his full senior debut.
A crowd of 6,730 saw Martin Hinshelwood's men relinquish their proud Saturday record at Withdean to two goals in the space of ten minutes for the Canaries in the second half.
Pint-sized former Spurs front man Paul McVeigh broke the deadlock on 58 minutes, nodding in his third goal in as many games after a remarkable save by Michel Kuipers from a Iwan Roberts header.
Midfielder Clint Easton killed off the battling Seagulls on 68 minutes with a spectacular left foot volley from Phil Mulryne's deep cross.
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