Charlie Austin's 93rd-minute penalty denied 10-man West Ham a hard-earned Premier League point as Southampton escaped with a 3-2 win at St Mary's on Saturday.
Javier Hernandez looked to have secured a fantastic draw with a brace either side of half-time after the Saints surged two goals ahead, but Pablo Zabaleta's push on Maya Yoshida enabled substitute Austin to snatch all three points with effectively the last kick of the match.
Southampton had earlier opened up a two-goal lead as Manolo Gabbiadini found a way past Joe Hart after 11 minutes. The Hammers then lost Marko Arnautovic to a straight red card for catching Jack Stephens with his arm before Dusan Tadic made it 2-0 from the spot.
However, Hernandez appeared to be Slaven Bilic's saviour by cutting the deficit before half-time and then added an equaliser with around 16 minutes remaining, opening his account in thrilling fashion following his close-season move from Bayer Leverkusen.
But Austin stepped off the bench to roll in a late winner from the spot and give Mauricio Pellegrino a first league victory as Saints boss.
FULL TIME: 3-2 's last-gasp penalty gives Mauricio Pellegrino his first win! Get in there August 19, 2017
Bilic handed a first start to 18-year-old Declan Rice as he rung the changes following the 4-0 defeat at Manchester United, although his plans suffered a setback when Winston Reid sustained a calf injury in the warm-up.
Michail Antonio made his return from a lengthy hamstring injury and the winger looked lively from the outset, teeing up Arnautovic for a good early chance before heading a corner into the arms of Fraser Forster.
West Ham's encouraging start quickly came to an end, though, as Nathan Redmond put a smart pass into space for Gabbiadini, who raced into the area and swept a clean left-foot finish across Hart.
Arnautovic should have done better again when Hernandez whipped an enticing ball in behind the defence, but the Austrian's stooping header was well smothered by Forster.
Tempers began to flare with Mario Lemina at the centre of a couple of heated exchanges, catching Arnautovic with a stray arm before receiving an unpunished studs-up challenge from Mark Noble. The tension proved too much for Arnautovic as the winger caught Saints defender Stephens in the face with his arm and was promptly shown a straight red card – just as he was against the same opposition while at Stoke City last season.
His petulance was compounded within five minutes as former Saints defender Jose Fonte dragged down Steven Davis in the area, allowing Tadic to fire the spot-kick through Hart's legs.
There was still time for the Hammers to pull one back on the stroke of half-time with Hernandez punishing Forster for failing to hold Antonio's half-volley.
Gabbiadini exploded back into life on the hour as his long-range attempt crashed against the crossbar, while Tadic was also denied a second by Hart's sharp near-post save.
Those near-misses appeared costly when Hernandez again showed his poacher's instinct, tucking away at point-blank range after Forster pushed Diafra Sakho's effort against the bar.
A stunned Southampton only recovered in the closing moments, with Redmond shooting against the crossbar before Austin was gifted the chance to seal a dramatic victory.
90: YES! YES! YES! makes no mistake from the spot. (3-2) August 19, 2017
