The Hammers were fortunate to come in at the break only 1-0 down, courtesy of Carl Jenkinson’s own-goal, after a dreadful first-half display.
However, Upton Park boss Bilic threw on fit-again Andy Carroll and Manuel Lanzini for the second half, swinging the game in their favour.
Michail Antonio grabbed a lucky equaliser before Carroll — back from yet another injury lay-off and sporting a bizarre, corn row-style hairdo — nodded in the winner.
“As long as he scores goals I don’t care about his hairstyle,” said Bilic. “It was the players who changed the game. Otherwise you could ask what I told them before the game to make them play so bad. It was them who changed the character, the approach.
“At half-time I didn’t tell them to go out and win the game, I just asked them to go out and give Southampton a game, because we were really poor, it couldn’t have been worse. In the end, though, I thought we totally deserved it.”
Southampton scored with virtually their first attack after 13 minutes when Dusan Tadic got in front of Jenkinson to get a toe onto Shane Long’s cross, with the ball rolling over the goal-line via the Hammers defender’s shin.
However, West Ham were transformed after the break and it was Antonio, something of a figure of fun this season, who grabbed an equaliser in comical style for his first goal for the club. The winger, dubbed the ‘missing man’ after chairman David Gold inadvertently retweeted a photo of him posted by a prankster looking for information about a missing friend, embarked on a mazy run into the area in the 69th minute. Antonio over-ran the ball and promptly fell over, but when Wanyama charged in to avert the danger his clearance hit the floored player on the head, looped up over Saints keeper Maarten Stekelenburg and into the net.
Then Carroll, in front of watching England boss Roy Hodgson, made up for a bad earlier miss with 11 minutes to go when he nodded in the rebound after Antonio had headed Enner Valencia’s cross against a post.
Saints boss Ronald Koeman, whose side had thumped Arsenal 4-0 on St Stephen’s Day, admitted Carroll’s introduction was the difference.
“It’s not too difficult to explain,” he said. “We spoke at half-time about our first half and what we could expect in the second half. It was a different opponent with Carroll on the pitch: More aggressive, more direct football, and that’s more difficult. You need to control the game and in the first 20 minutes of the second half we lost more balls and made more mistakes and, out of two situations, that’s the reason we lost.”
Adrian, Tomkins, Collins, Ogbonna, Jenkinson, Song (Lanzini 46), Kouyate, Antonio, Noble, Zarate (Carroll 46), Valencia (Obiang 86).
Stekelenburg, Martina (Yoshida 70), Fonte, van Dijk, Bertrand, Wanyama, Romeu, Tadic (Ramirez 75), Mane (Juanmi 75), Steven Davis, Long.
Michael Oliver (Northumberland).