Collison marked his return to the starting line-up with goals in the eighth and 41st minutes to silence a fervent home crowd and put the away side in a favourable position heading into the second leg on home turf.
Nevertheless, with the away goals rule non-existent in the Football League's annual promotion knock-out, a close call for Carlton Cole and a missed header from seemingly unmissable range by skipper Kevin Nolan may end up coming back to haunt the Hammers should the Bluebirds pull off a fight-back with a powerful away performance of their own.
Cole cleared an effort from Mark Hudson off the line at the other end, but Cardiff boss Malky Mackay, a former United player, looked frustrated from the technical area as his men failed to utilise their home advantage and face an uphill struggle if they are to return to Wembley following their Carling Cup final defeat against Liverpool as well as appearances in 2008 and 2010.
Seeking to make good on their home leg as soon as possible, the Blues burst out of the blocks with confident attacking play and almost took the lead inside the opening minutes.
Aron Gunnarsson’s dangerous long throw into the West Ham area was only half-cleared by Nolan and Peter Whittingham’s strike was deflected over the crossbar.
The ensuing corner was sent back in following a routine clearance and Kenny Miller’s fierce half-volley from a tidy nod-down was pushed around the upright by Rob Green.
But Sam Allardyce’s troops did well to ride their luck early on and the reward was prompt: in-form forward Ricardo Vaz Te did well to put in a cross from the left before the ball could cross the byline and though Collison’s initial effort was superbly blocked point-blank by goalkeeper David Marshall, the 23-year-old headed home the rebound to break the deadlock.
The goal knocked the stuffing out of the hosts, who came into the game evidently expecting to control the tempo within their own four walls, and the Irons did well to suffocate their game.
Miller tried hard to carve out chances where he could, but the key stats all favoured the away team and with four minutes remaining until the interval, things went from bad to worse for the Welsh club.
After Hudson had denied Cole a one-on-one with Marshall at the expense of a corner, the set piece was headed away from goal and into the path of Collison, whose chested-down volley deflected off the head of a defender and left Marshall wrong-footed as the ball detoured beyond him.
One of many sublime crosses from Matt Taylor was met by the head of Cole in the final minute of the half, and only a superb parry from Marshall prevented it from finding the bottom corner and the half-time whistle was a welcome relief for the shell-shocked home side.
Cardiff managed to open up the game a little more in the second period, and 10 minutes in a Whittingham corner was headed towards goal by Hudson, where Cole was well-positioned to keep the effort out in a role-reversal between defender and attacker.
With 20 minutes spare, Nolan forced another good block from Marshall with a header from Mark Noble’s free-kick from the left, and two minutes later another inch-perfect Taylor delivery was somehow nodded off target by the captain from even closer to goal.
Taylor went low with his cross on 77 minutes and was inches away from picking out the outstretched leg of Cole, and with five minutes remaining Joe Mason volleyed a big chance for a Cardiff lifeline over from close range after a corner kick had been headed into his path.
West Ham take the 2-0 lead into the second leg which kicks off in the late afternoon on Bank Holiday Monday at Upton Park.