West Brom moved up to second place in the Coca-Cola Championship as they became the first visiting team since August to win at Colchester's Layer Road ground.
After losing their first two home matches, Geraint Williams' side had gone 14 games without a home defeat but Paul McShane and Diomansy Kamara struck in the space of two second-half minutes to end that run.
Johnnie Jackson pulled one back almost straight away but there was to be no way back for the U's as the Baggies climbed above Birmingham into second spot.
Colchester were unchanged from the side that won impressively at Barnsley on Saturday while the Baggies made two changes as John Hartson and Darren Carter replaced Kevin Phillips and Jason Koumas respectively.
The Baggies had the first effort on goal when Richard Chaplow fired in a low shot which Kem Izzet deflected wide, and Neil Clement headed over from the resulting corner.
Kamara then fired wide from 20 yards out, while Wayne Brown had to be alert to make a good block after Kamara and Hartson had linked up well.
The first shot on target came midway through the opening period but Dean Gerken in the U's goal was equal to Carter's effort and Chaplow fired wide of the target from fully 30 yards, before a Carter corner hit the post and bounced clear.
That seemed to spark the home side into life and they finally fashioned an effort just after the half-hour but Jamie Cureton's effort failed to trouble Dean Kiely in the visitors' goal.
Jackson did manage to test Kiely moments later but his 25-yard effort was saved comfortably by the former Portsmouth stopper, before Izzet fired wide from distance.
The visitors began the second half brightly and Hartson sent a left-footed shot narrowly wide of the post inside the first 30 seconds of the second period, before Zoltan Gera sent a 30-yard effort over the bar.
And they were rewarded five minutes into the second half when Robert Koren's corner from the left was turned in by McShane for his first league goal for the club.
It was two just two minutes later when Kamara beat Gerken with a smart close-range finish for his seventh goal in his last six matches from a Chaplow pass.
But the U's hit back almost straight away when the Kevin Watson's corner was flicked on to Jackson and he fired home his first goal for the club.
The U's threw caution to the wind shortly after as striker Richard Garcia came on for defender John White as the home side tried to get back into the encounter.
And Cureton came close to bringing them level with a 20-yard effort which Kiely had to tip over his bar.
But it was the visitors who really should have grabbed the game's fourth goal when another Koren corner was met by McShane six yards out, but his header went over the crossbar.
Curtis Davies then broke through but was denied by the feet of Gerken, while at the other end Kiely had to make a fine save to deny Chris Iwelumo after Karl Duguid had played him in.
McShane then saw another header - this time from a Carter corner - saved by Gerken and substitute Sherjill MacDonald's shot was also claimed by the U's stopper.
The Dutch striker also fired wide from 20 yards, Gerken denied Kamara and Koren had an effort blocked by Garcia as the Baggies saw out the game to claim a vital three points.
Teams:
Colchester Gerken, White (Garcia 58), Mills, Brown, Barker,Duguid, Watson, Izzet (McLeod 76), Jackson, Iwelumo, Cureton.
Subs Not Used: Cousins, Baldwin, Ephraim.
Booked: Izzet.
Goals: Jackson 55.
West Brom Kiely, McShane, Curtis Davies, Clement, Robinson,Gera, Carter, Chaplow, Koren, Hartson (MacDonald 76), Kamara.
Subs Not Used: Daniels, Albrechtsen, Koumas, Hodgkiss.
Booked: Carter, McShane.
Goals: McShane 51, Kamara 52.
Att: 5,611
Ref: M Atkinson (W Yorkshire).