Watford stretched their lead at the top of the Championship to four points with a convincing win at Scunthorpe.
Adam Johnson headed Watford ahead from Lloyd Doyley's free-kick but the hosts were level at half-time thanks to Jonathan Forte's clever chip.
Darius Henderson tapped in after 61 minutes to make it 2-1 before Marlon King wrapped up the scoring when Joe Murphy failed to hold his shot.
Lee Williamson's red card for a wild tackle was Watford's only sour note.
Scunthorpe manager Nigel Adkins:
"We put up a good show and will try to take the positives.
"It was mission impossible and we've proved that whoever comes here will need
to be on top of their game to get the points.
"The fans have seen a totally committed bunch of players giving their all."
Watford boss Aidy Boothroyd:
"I was excited about coming to this place because it's a proper club.
"We've tasted the prawn sandwiches at the big corporate clubs and I'm sure
Scunthorpe will do ever so well.
"We knew it would be difficult but we coped with what they had and won."
Scunthorpe: Murphy, Byrne (Cork 85), Crosby, Butler, Youga, Taylor (Hayes 68), Goodwin, Sparrow, Hurst, Forte (May 79), Paterson.
Subs Not Used: Lillis, Iriekpen.
Booked: Forte, Byrne, Crosby.
Goals: Forte 20.
Watford: Lee, Doyley, Shittu, DeMerit, Stewart, Smith, Mahon, Williamson, Johnson (McAnuff 70), King (Priskin 82), Darius Henderson (O'Toole 76).
Subs Not Used: Ellington, Mariappa.
Sent Off: Williamson (75).
Booked: Darius Henderson, Smith, O'Toole.
Goals: Johnson 10, Darius Henderson 61, King 63.
Ref: Eddie Ilderton (Tyne & Wear).