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:
A message from the Football Clubs Editor
Our aim is to provide you with the best, most up-to-date and most informative Newcastle United coverage 365 days a year.
This depth of coverage costs, so to help us maintain the high-quality reporting that you are used to, please consider taking out a subscription; sign up here.
Your support is much appreciated. Richard Mennear, Football Clubs Editor