Steve Bruce’s side took the lead in the first half through Sean Longstaff’s stunning strike – his first in 14 months.
Chances were squandered before Ismaila Sarr equalised for the hosts on 72 minutes.
The Hornets celebrated a winner, that was until VAR ruled out Josh King’s goal for offside.
Substitute Jacob Murphy went one-on-one with Ben Forster in the final seconds of the match but his chipped attempt was read by the goalkeeper.
Our man Miles Starforth was at Vicarage Road – and he has dished out his Newcastle player ratings:
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The Hornets celebrated a winner, that was until VAR ruled out Josh King’s goal for offside.