Matt Sparrow scored twice as Rickie Lambert's sending off proved to be the turning point in Brighton's victory over Championship leaders Southampton.
Lambert was sent off in the 51st minute after an altercation with Adam El-Abd.
Jake Forster-Caskey, on his full debut, put Brighton ahead, slotting home after Kelvin Davis denied Kazenga LuaLua.
Sparrow fired home a stunning 35-yard strike and added another emphatic finish before captain Gordon Greer was dismissed for an off-the-ball incident.
Saints, who went into the game on the back of a first home defeat in more than a year, only stay top of the league on goal difference following West Ham's 1-0 win over Coventry, while Brighton ended their run of four successive defeats without scoring in emphatic style.
The visitors dominated the first half but were outplayed once Lambert, the division's leading goalscorer, was sent off for the first time in his career.
The hosts, missing 10 players through injury and suspension, were instantly spurred on and Saints had goalkeeper Davis to thank after he impressively denied LuaLua.
However, he was beaten moments later as Forster-Caskey netted the rebound after Davis had initially kept out LuaLua's stinging effort.
Sparrow's magnificent goal then added to the hosts' joy and he added another by firing into the top corner from just inside the area after a goalmouth scramble.
Greer's sending off three minutes from time, the fifth red card shown to a Brighton player this season, following an incident with substitute Jonathan Forte, was the only disappointing aspect of the Seagulls' display, but it mattered little.
The Saints could have scored in the first half but Peter Brezovan made a fine save to deny David Connolly and Guly Do Prado somehow blazed over from six yards.
Lallana was also denied a goal when his effort appeared to cross the line, prior to Steve Cook's clearance.
Southampton manager Nigel Adkins: "The sending off of Lambert was a massive turning point as we were in control of the match at that time. It changed the whole complexion of the game.
"I have looked at the video and although it's not a great view, the lad (El-Abd) stopped Rickie getting up. It's a poor video but Lambert hasn't lashed out.
"The referee had a better view and there's no doubt it was a defining point.
"We need to win the next one. We're being challenged from a results point of view."
Brighton manager Gus Poyet said: "There is no better way to start the year. From a fan's point of view, apart from the win against Crystal Palace, it doesn't get any better.
"I'm delighted with the result after our recent run of results. It's all about decisions and fortunately they worked well so I'm pleased."