Not long later, Watford took the lead again. King chased the ball to the byline, playing a low, drilled pass to Sarr, who converted from close range for his first away goal of the season.
Dennis wasn’t far off grabbing his second and Watford’s third when Sarr’s swooping delivery went across goal and was inches from meeting the winger’s boot.
Norwich’s Milot Rashica then forced Foster into action with a powerful strike, but the Watford goalkeeper made an impressive stop to deny the Kosovo international.
With 15 minutes left to be played, the drama was far from over.
King came close to scoring his first goal in a Watford shirt, but Krul parried. Sarr, reacting quickly, fired in the rebound, prompting celebrations in the away end and on the touchline.
Initially, the assistant referee’s flag denied the Hornets a two-goal cushion, but VAR corrected the call and confirmed the goal was onside.
Substitute Ken Sema was next to break into the box, beating two on the dribble before defender Ozan Kabak prevented a fourth goal.
A successful away day for Xisco Muñoz’s men was almost capped off by a hat-trick for Sarr, but Krul was there to deny the Senegal international.