Darius Henderson scored a goal in each half to earn promotion hopefuls Watford their first win in five matches.
On both occasions, Henderson was perfectly-positioned at the far post to head in crosses first from Anthony McNamee and then from Ashley Young, the second effort restoring Watford's lead after Nicky Forster's second-half equaliser for Ipswich.
The victory allows Watford to remain in the top two play-off spots, which would ensure they played the second leg of a semi-final at home.
Henderson's goals proved Watford can cope without suspended top scorer Marlon King, which would have impressed the watching Kevin Blackwell, manager of the Hornets' play-off rivals Leeds.
Although their play-off spot was secure, Watford had no intention of taking a breather and pushed Ipswich, who had made six changes, back from the beginning.
Clarke Carlisle came desperately close to giving the home side the lead in the sixth minute, first heading the recalled McNamee's right-wing corner against the bar and then drawing a fine save from Lewis Price with his follow-up effort.
But Ipswich, with their more patient approach work, twice forced excellent stops from Ben Foster, the on-loan Manchester United goalkeeper blocking fierce drives from Alan Lee and Forster.
Watford eventually seized the lead after 32 minutes. The lively Al Bangura won the ball in midfield, allowing Chris Eagles to feed McNamee on the left, and Henderson was there to head in the winger's fine cross at the far post.
Ipswich - who were poor in the first half - brought on Danny Haynes and Darren Currie for Dean Bowditch and Vermund Brekke-Skard for the second period, switching from 4-5-1 to 4-4-2.
Joe Royle's tactical switch quickly paid dividends. A more purposeful Ipswich side believed they should have had a penalty in the 58th minute when Lee went down under Malky Mackay's challenge - and 60 seconds later they were level.
The clever Currie's free-kick from the right was flighted perfectly for Forster to head powerfully past Foster from close range.
Henderson had a goal ruled out for offside in the 62nd minute because team-mate Mackay was in an illegal position when Young delivered his free-kick, but he earned his reward for a hard-working performance 12 minutes from time.
Lloyd Doyley released Young on the right, and from the youngster's cross Henderson planted a firm header beyond Price at the far post.
Teams
Watford: Foster, DeMerit, Mackay, Carlisle, Doyley,Eagles (Chambers 70), Mahon, Bangura, McNamee (Stewart 81),Young, Henderson.
Subs Not Used: Chamberlain, Mariappa, Robinson.
Booked: Mackay.
Goals: Henderson 33, 77.
Ipswich: Price, Richards, De Vos, McEveley, Naylor, Sito,Bowditch (Currie 45), Juan, Brekke-Skard (Haynes 45), Forster,Lee (Peters 88).
Subs Not Used: Supple, Wilnis.
Booked: Lee.
Goals: Forster 57.
Att: 16,721
Ref: C Webster (Tyne & Wear).