Cameron Archer thought he had put the Saints ahead before VAR reviewed the build-up to the goal
Southampton were furious after being denied a priceless victory by a controversial VAR decision in a 1-1 draw at Brighton.
Flynn Downes had just cancelled out Kaoru Mitoma's opener when Cameron Archer converted a cross from Saints substitute Ryan Fraser.
A VAR check of more than four minutes eventually decided Archer was onside but then penalised Adam Armstrong, who was offside but did not touch the ball, for interfering with play.
It meant Saints, still rock bottom of the Premier League, had to settle for a first away point of the season.
A point was enough to lift Brighton up to second, however, level on points and goal difference with Manchester City.
The hosts dominated the first half but only had Mitoma's goal to show for it.
They almost took the lead following an early Southampton corner, with Yasin Ayari leading the break before aiming for Mitoma.
Defender Yukinari Sugawara should have dealt with the pass but was knocked off the ball by his Japan colleague. With Saints keeper Joe Lumley, making his Premier League debut, hastily back-pedalling into position Mitoma probably should have scored, but he could only steer his finish wide.
Georginio Rutter's drive then whistled past Lumley's right-hand post, before the midfielder went even closer when his curler clipped the opposite upright.
The opening goal Brighton's pressure merited arrived in the 29th minute following a cross from fit-again right-back Tariq Lamptey.
The ball actually bounced in front of Mitoma, but he threw himself forward and powered a spectacular header past Lumley and into the net.
Southampton could have snatched an equaliser through Archer just before the interval.
Evan Ferguson and Ryan Manning (bottom, right) both featured in the match
The striker met a dangerous cross from Sugawara at the near post, but the ball bounced up on to his shin and flew wide.
However, Saints did haul themselves level 13 minutes into the second half with the impressive Tyler Dibling the architect.
The teenager's square ball teed up Armstrong, whose shot was blocked, as was his follow-up effort. But the loose ball found its way to Downes, who hammered it home first time from the edge of the area.
Eight minutes later Dibling brilliantly wriggled clear of three Brighton players inside his own half and then spread the ball to Fraser.
The midfielder's low cross evaded Armstrong and was finished at the far post by Archer - only to be chalked off to the dismay of boss Russell Martin.
The official explanation was that "Armstrong was in an offside position and deemed to be impacting (goalkeeper Bart) Verbruggen's ability to play the ball".
There was more drama towards the end of 13 minutes of added time when Seagulls sub Simon Adingra's effort beat Lumley but flicked the outside of the far post.
Republic of Ireland striker Evan Ferguson was a 79th minute substitute for Brighton, while Boys in Green left-back Ryan Manning started for Southampton.