Jos Hooiveld's late equaliser rescued a point for Southampton as the Championship's top two clubs shared the spoils at Upton Park.
Mark Noble put the Hammers in front from the penalty spot before the break after being fouled by Billy Sharp.
The Saints striker was also involved in an incident that saw Matt Taylor sent off shortly before West Ham's goal.
Sharp was later denied by Rob Green but Saints equalised when Hooiveld poked home from close range.
The result saw leaders West Ham maintain their one-point advantage over Saints, but both sides missed the opportunity to strike a significant blow on their nearest rival in the race for automatic promotion.
In fact, the draw allowed the chasing pack back into the mix as Cardiff City and Blackpool both won to close the gap on the top two.
Saints' poor away record continues with Nigel Adkins' side still without a victory on the road over a side in the top half of the table.
Nonetheless, Adkins will see it as a point gained considering his side's poor start to the game, while his opposite number Sam Allardyce will point towards Taylor's disputed red card as the game's turning point.
Still, Allardyce's side remain top and it will take something special to prevent them from returning back to the Premier League at the first attempt based on tonight's evidence.
Just a point separated these two sides before the game but the gulf in class during the opening stages could not have been greater.
West Ham outclassed, outmuscled and outplayed their opponents early on but once Taylor had been dismissed, a combination of great goalkeeping from Green and poor finishing from Sharp prevented Saints clawing their way back into the contest.
West Ham came flying out of the traps with Ricardo Vaz Te testing Kelvin Davis with a fierce half-volley in the opening minute and they soon took the lead with a hotly-disputed penalty.
Sharp was harshly adjudged to have brought down Noble and then became involved in an altercation with Taylor. The Saints striker collapsed to the floor in a heap and referee Lee Probert handed a red card to the unfortunate Taylor 18 minutes into the game.
Noble kept his cool to convert from the spot but with a man advantage Saints came back into the game.
Recent signing Sharp should have levelled but struck Green from close range and the Hammers keeper later pulled off a fine one-handed save from Rickie Lambert's 18-yard shot.
West Ham started the second half brightly but Lambert came close to connecting from close range as the visitors pressed for an equaliser.
Hooiveld headed a Saints corner over from close range when he really should have tested Green, but the big Dutchman made amends moments later when poking home Lambert's knock down from six yards out.
The Hammers introduced debutant Nicky Maynard from the bench and the former Bristol City man forced a decent save from Davis with five minutes remaining.
It was the last meaningful action of a pulsating contest which leaves the race for promotion well and truly open.
VIEWS FROM THE DRESSING ROOM
West Ham manager Sam Allardyce:
"The Southampton player has held his face when Matt Taylor pushed him in the chest.
"The assistant referee has been conned and unfortunately we lost a man from then on.
"But the biggest problem was the referee missed two of the most blatant penalties you will ever see. Everyone in the ground could see they were penalties."
Southampton boss Nigel Adkins:
"It was a good game of football with lots of incident.
"At the end of the day we've come away from home and got a point. We've totally dominated the game on the balance of play.
"We should have got a penalty of our own in the second half. I've watched it again and it was a clear penalty."