The Welshman, a product of the London club's youth system, registered twice at the Cardiff City Stadium, nodding home from close range after nine minutes and then seeing his deflected volley find the back of the net four minutes before the break to give the Hammers a huge advantage going into the second leg on Monday.
The hosts struggled for any kind of rhythm for much of the match and West Ham could have taken an even more comfortable lead back to Upton Park, but for David Marshall's superb save from Carlton Cole's header.
The Hammers may still have two more games to negotiate before they can celebrate a return to the top flight but, on this showing, the class and determination is there to achieve exactly that.
Cardiff almost went ahead after two minutes, Peter Whittingham's deflected effort dipping narrowly over the crossbar.
Moments later, Robert Green had to be alert to beat away Kenny Miller's volley as the Bluebirds started at a furious pace.
But with their first attempt at goal, the Hammers gained the upper hand. Ricardo Vaz Te crossed from the left and, although Collison's first attempt was brilliantly stopped by Marshall, the Welshman was on hand to nod in the rebound.
Quickly, West Ham got a stranglehold on the game. Gary O'Neil tested Marshall from range and James Tomkins headed Matt Taylor's fizzing cross wide.
Cardiff, in part, were the architects of their own struggles, frequently gifting possession to their guests.
The Welsh side tried to rally, with Miller firing wide, but Collison soon stunted their comeback with his second.
Taylor's corner was half-cleared to the midfielder, who controlled the ball on his chest, pulled the trigger and saw a wicked deflection off the head of Liam Lawrence wrongfoot Marshall.
Cole must have thought he had put the tie out of sight before half-time, but Marshall pulled off a sensational low save from the striker's header.
Cardiff showed intent to get back into the game after the interval, with Whittingham volleying wide and Ben Turner seeing his header cleared off the line by Cole, before Miller fired horribly off-target.
With space tighter in the Cardiff half, West Ham created far fewer chances - the best of the lot being Kevin Nolan's point-blank header which failed to test Marshall - and the visitors had to withstand a spell of concerted pressure from their hosts in the final quarter.
Mark Hudson nodded Aron Gunnarsson's cross wide from 10 yards, substitute Robert Earnshaw missed the target with a wild volley and Gunnarsson squandered a decent chance from the edge of the area.
For all their late huff and puff, however, the Bluebirds could not fashion a goal, leaving themselves with a lot to do in London in four days' time.