Scott Vernon struck twice as Colchester clung onto their Championship status for another week and dealt a blow to Ipswich's play-off hopes.
The Us forward struck in each half at Layer Road to notch his sixth and seventh goals of the season to end a run of 10 games without a victory.
Vernon fired into the bottom corner from 12 yards after 29 minutes to opening the scoring and wrapped up the points 17 minutes from time with another assured finish.
Ipswich kicked off knowing a win would move them back into the play-offs and it was they who began the more purposefully.
Less than two minutes had passed when Owen Garvan delivered a dangerous inswinging corner but Us goalkeeper Dean Gerken punched to safety.
Town midfielder Gavin Williams tried his luck from 18 yards in the sixth minute as Jim Magilton's side pushed for an opener but his effort flew past the left post.
The home side had their first real chance of the game in the 14th minute after Johnnie Jackson had been fouled by Luis Castro Sito, who earned a booking for the offence.
Karl Duguid took the resulting free-kick from 20 yards but failed to trouble Ipswich goalkeeper Stephen Bywater.
The Us began to take control and Vernon could count himself unfortunate when his header from Dean Hammond's free-kick flashed past the right post.
Twice in the space of three minutes Gerken made comfortable saves to deny Lee and soon afterwards Geraint Williams' side took the lead courtesy of Vernon.
Lee and Danny Haynes both spurned further opportunities as United, who had conceded 12 goals in their previous three games, hung on until the break.
The second half was slow to get going. Alan Quinn attempted an ambitious effort from 25 yards which flew wide of the post.
Magilton brought on Gary Roberts and Jordan Rhodes in a bid to swing the game in his side's favour but it was Colchester who looked the more likely to add to their lead.
Jackson came close with an 18-yard drive just after the hour mark and by the 73rd minute Vernon had doubled the advantage.
It was another clinical finish, again into the bottom corner but this time from the edge of the area.
The Tractor Boys' away form has proved costly all season - they have won on their travels just three times in the league all season - and they rarely troubled Gerken.
Roberts failed to find the target with his 25-yard free-kick and Williams skewed an effort over the crossbar.
Tommy Miller was thrown on with five minutes remaining but it was too little, too late.
Gerken saved well from Rhodes but it was Colchester striker Kevin Lisbie who almost had the final say, twice firing 18-yard efforts narrowly wide.
Teams:
Colchester Gerken, Ifil, Coyne, Heath, White, Duguid, Hammond, Jackson, Elito, Lisbie, Vernon.
Subs Not Used: Izzet, Kevin McLeod, Guy, Balogh, Cousins.
Goals: Vernon 29, 73.
Ipswich Bywater, Simpson, De Vos, Bruce, Sito, Williams (Miller 85), Garvan, Sumulikoski (Rhodes 62),Quinn (Roberts 58), Haynes, Lee.
Subs Not Used: Colgan, Wright.
Booked: Sito.
Att: 6,264
Ref: Andy D'Urso (Essex).