Just when it looked like the Hammers had ploughed the Tractor Boys into play-off oblivion, battling Ipswich Town rose from the dust to keep this semi-final wide open.
Two goals inside the opening 13 minutes from Marlon Harewood and Bobby Zamora seemed to have set West Ham well on the road to Cardiff, but Joe Royle's side - who were eliminated by the East Enders at this stage last year - fought back to secure a draw thanks to a James Walker own goal and Shefki Kuqi's late leveller.
West Ham came into this game unchanged from the side that had guaranteed their play-off place with a 2-1 win at Watford last weekend, while Ipswich made two switches from the team that drew at Brighton, as ex-Hammers David Unsworth and Darren Currie were replaced by former Upton Park midfielder Kevin Horlock and Drissa Diallo.
Three places and 12 points had separated these sides across the 46-game campaign. But within just 13 luckless minutes, Town had found that gap closed as West Ham - backed by a raucous roar - took a two-goal lead thanks to two lightning left-wing raids by Matthew Etherington.
On seven minutes, the West Ham wide boy outpaced Diallo in the race to gather Walker's huge clearance upfield and, when he crossed into the six-yard box, the unmarked Harewood got the better of the tumbling Richard Naylor to slide in his 22nd goal of the season.
And with 13 minutes on the clock, the Upton Park noise levels reached fever pitch as Etherington again showed Diallo a clean set of studs, and when his cross into the six-yard box was only half-cleared by Jason De Vos, Zamora was in the right place at the right time to drill home from ten yards.
Both Harewood and Zamora might have found the net again, before Darren Bent unleashed a couple of low goalbound efforts that came to nothing, while Kuqi looked to have summed up the shell-shocked Tractor Boys' first half when he finally mustered a shot which curled so wide it went for a throw-in.
With Hammers looking set to canter off with a comfortable two-goal lead deposited in their locker, the reckless Tomas Repka - playing his last game at Upton Park prior to being released by the club - ridiculously shoved over Kuqi 18 yards out.
And after collecting the 53rd yellow card of his Hammers career for furiously debating the award with referee Uriah Rennie, the Czech paid a double penalty.
Tommy Miller's consequent free-kick deflected off Repka's foot and onto the base of Walker's left-hand post, before unluckily hitting the grounded keeper on the back and crossing the line to give Town second-half hope.
Passions were now running high as Alan Pardew and Joe Royle exchanged heated words in the cauldron of tension, but the Ipswich boss gathered his head to make a telling double switch at half-time, as Diallo was replaced for his own protection, alongside Horlock, to be replaced by Matt Richards and Currie.
On the hour, Anton Ferdinand met Shaun Newton's well-flighted cross with a downward header that Kelvin Davis miraculously palmed skywards and with that Hammers' superiority disappeared into the East East air, too.
For with the momentum deserting the home side, Ipswich grew in self-belief and after Currie's 71st-minute left-wing free-kick was athletically clawed out from underneath his left-hand angle, the Portman Road outfit secured that precious equaliser.
With just 16 minutes left, another deep Currie ball from the left fell to Bent whose shot looped up off Chris Powell only for Walker and Ferdinand to get in each other's way. That left Kuqi to blast home the equaliser from six yards, to leave both sides with everything still to play for at Portman Road on Wednesday evening.