Premier League player of the month Michail Antonio was shown a late red card as West Ham missed the chance to go top of the table after scraping a goalless draw at winless Southampton.
Antonio was dismissed for a second yellow card deep into added time following a late tackle on Moussa Djenepo having earlier been booked for a tangle with Jack Stephens.
Tottenham's 3-0 defeat at Crystal Palace in Saturday's lunchtime kick-off had opened the door for the Hammers to climb to the summit with victory at St Mary's.
But David Moyes' unbeaten side were lucky to escape with a point as lively Saints substitute Armando Broja struck a post and had a header hacked off the line late on.
Adam Armstrong and Nathan Redmond also had decent openings for Ralph Hasenhuttl's hosts, who registered a third consecutive draw, while Antonio, Tomas Soucek and Jarrod Bowen had the visitors' best openings.
With a Europa League campaign to contend with this term, West Ham's visit to the south coast marked the start of seven games in 23 days.
Hammers boss Moyes resisted temptation to rotate, naming an unchanged starting XI for the fourth successive game and leaving new signings Kurt Zouma, Alex Kral and Nikola Vlasic awaiting debuts from the bench.
United had won six of the past seven meetings but there was little to separate the two sides during a forgettable first half.
The visitors shaded possession, yet a tame early shot from increasingly-isolated Southampton striker Armstrong was the sole attempt on target.
West Ham's lack of attacking threat was surprising given they came into the contest having scored 10 times in their opening three games, a record matched only by champions Manchester City.
In-form Antonio contributed heavily to that statistic with four goals and three assists and he eventually threatened two minutes into the second period.
The away side broke swiftly following a Saints corner, culminating in the 31-year-old – who had a loan spell at St Mary's 12 seasons ago – stinging the palms of home goalkeeper Alex McCarthy with a low effort which looked set to sneak inside the right post.
That attempt helped inject some much-needed tempo into proceedings.
Around 3,300 travelling fans behind McCarthy's goal – who were revelling in rivals Spurs losing at Selhurst Park – were then poised to celebrate but the towering Soucek somehow failed to connect with a corner, before Saints winger Redmond was unable to capitalise on a rapid counter-attack.
Eager to exploit his team's growing superiority, Moyes sent on creative Croatia midfielder Vlasic, who arrived on deadline day from CSKA Moscow for a reported £27million, with 27 minutes remaining.
Shortly after, McCarthy tipped over a volley from Bowen and it seemed only a matter of time before the breakthrough arrived.
Yet, momentum swung back the other way and the Hammers would be grateful to leave with their unbeaten record intact.
Chelsea loanee Broja – born in Slough to Albanian parents – was changing the course of the game, causing constant problems for the Hammers with his direct running.
With just under 10 minutes remaining, the 20-year-old moved the ball away from the retreating Angelo Ogbonna, only to see his well-struck effort rebound off the left upright.
Fellow substitute Ibrahima Diallo then fired over, before the Hammers were reliant on captain Declan Rice to clear Broja's goal-bound header off the line.
With a congested fixture list to come, Moyes would perhaps have been relieved to come out of this contest relatively unscathed.
But he was then deprived of the services of star man Antonio for next weekend's visit of Manchester United after the forward foolishly lunged at Djenepo five minutes into time added on.
