The 20-year old Czech striker, on a season-long loan from Udinese, scored in stoppage time of the first half and added a second with seven minutes remaining to make it six goals in his past four Championship outing for the Hornets as they remained sixth on the table.
Vydra has now netted 14 goals in 23 appearances for Gianfranco Zola's men with the Italian manager suggesting he could have had even more at the Riverside Stadium on the weekend.
"Matej should have had more really. It's unusual to see him miss. I'm not too mad, if he keeps playing like that he'll soon be scoring a hat-trick," said Zola.