Roy Keane's visitors bossed the opening 40 minutes of an open game before the Hornets took control with two goals in two minutes before the break.
Stephen McGinn opened the scoring and Sordell then struck his sixth league goal in his last eight appearances to leave Ipswich with a mountain to climb.
David Norris headed in for the visitors after the break but Watford held on for an important three points.
Ipswich's Jason Scotland had the first chance of the night but blasted over from former Watford striker Tamas Priskin's flick on before the Hungarian raced onto a long ball but failed to get a shot away.
Keane's men looked menacing on the break and Scotland almost gave them the lead after a lovely turn but placed his curling shot a foot wide of the far post.
Unlike previous Watford sides, Mackay's men were perhaps guilty of overplaying at times and youngster Michael Bryan almost put them in trouble when an ambitious pass on the edge of his own area was intercepted.
Danny Graham then created the first chance for the hosts with a direct run down the left but his pass inside was easily cut out by Brian Murphy in the Town goal.
Graham was then narrowly wide with a header before McGinn struck the 41st-minute opener.
A long throw from the right was headed on at the near post by Martin Taylor and the midfielder was left with the simple task of volleying home from the six-yard line.
The hosts were buoyant and doubled the lead just two minutes later through Sordell.
Andrew Taylor crossed from the left and the Championship's young player of the month rose magnificently to flick a brilliant header over Murphy and into the top corner.
Watford began the second half in similar style, and Lloyd Doyley should have found a team-mate after bursting into the area.
Priskin was then replaced - to the delight of the home fans - by giant teenager Connor Wickham as Keane looked for a response.
And captain Norris handed the away side a lifeline in the 69th minute with a fabulous header.
Watford goalkeeper Scott Loach punched away a set-piece but was on the floor as Norris arched in a header from fully 20 yards with two defenders on the line.
And Keane's men almost grabbed an equaliser in the dying moments when substitute Ronan Murray touched in a Grant Leadbitter set-piece but the linesman's flag was already raised.