Teenager Danny Haynes struck late on to secure Ipswich victory in their first league meeting with Colchester at Portman Road in more than 50 years.
The 19-year-old striker drilled home a fine pass from Jaime Peters in the 82nd minute before spirited Colchester hit back at the death with a penalty from Chris Iwelumo.
The scores were tied at 1-1 at the interval, but Sylvain Legwinski rose to connect with Gavin Williams' corner in the 55th minute to put the Tractor Boys 2-1 ahead before Haynes came off the bench to add the killer third to ensure Iwelumo's penalty was nothing more than consolation.
Colchester had never played in English football's second tier until this season, but they began the day in seventh spot and with serious play-off ambitions.
And midfielder Karl Duguid threatened to write another chapter into their remarkable campaign when he opened the scoring after 15 minutes.
However, Alan Lee equalised from the penalty spot on the half-hour mark and Legwinski claimed his fifth goal of the season in the 55th minute before Haynes added the coup de grace with eight minutes remaining.
Despite missing 14-goal striker Jamie Cureton due to a hamstring stain, Williams' upstarts made light of his absence during a bright and inventive start.
Duguid, whose goal handed Colchester a 1-0 win against Ipswich at Layer Road last September, tried his luck from 25 yards in the sixth minute which required Lewis Price to make a smart stop.
Three minutes later, though, Ipswich engineered their first clear-cut opening when Richard Naylor headed wide at the far post from Gary Roberts' inswinging corner.
Peters then volleyed narrowly over Colchester's crossbar as the visitors again escaped before opening the scoring in the 15th minute.
Iwelumo was the architect, racing down the left flank before crossing low and hard for Duguid to drill the ball into the bottom corner from 12 yards.
Ipswich threatened an immediate riposte when Roberts curled a delightful free-kick that Colchester goalkeeper Dean Gerken parried to safety.
Naylor then headed wide before Jim Magilton's men drew level on the half hour mark.
A teasing cross from David Wright led to Garry Richards fouling Lee and the Ipswich striker stepped up to convert the resultant penalty.
And three minutes before the break it should have got even better for Ipswich as Roberts watched another superb free-kick bounce agonisingly back off the crossbar.
The impressive Roberts then connected with a cross from Legwinski but could only head straight at Gerken.
But 10 minutes after the restart Ipswich claimed the winning goal when Legwinski nipped in ahead of team-mate Alex Bruce to connect with Williams' corner and steer a neat header into the net.
The goal lifted the Tractor Boys and Lee was unlucky not to claim his second goal after seeing a vicious 20-yard volley just wide of the far post.
However, Haynes came on for Billy Clarke in the 67th minute and made his mark in the closing stages with an assured right-foot finish from 12 yards.
Colchester refused to surrender and Iwelumo blasted home from the penalty spot after Wright handled in the area and was subsequently dismissed - but Ipswich held on for victory.
Teams
Ipswich Price, Wright, Bruce, Naylor, Harding, Peters,Legwinski, Williams, Roberts (Richards 90),Lee (O'Callaghan 86), Clarke (Haynes 67).
Subs Not Used: Supple, Wilnis.
Sent Off: Wright (90).
Booked: Clarke, Williams.
Goals: Lee 30 pen, Legwinski 56, Haynes 82.
Colchester Gerken, Halford, Brown, Richards (White 86),Barker, Garcia, Watson, Izzet (Jackson 77), Duguid, Iwelumo,Ephraim (Guy 63).
Subs Not Used: Davison, Elokobi.
Booked: Halford, Brown.
Goals: Duguid 15, Iwelumo 90 pen.
Att: 28,355
Ref: G Laws (Tyne & Wear).