When the Belgian scored twice in the opening 17 minutes, Jurgen Klopp’s squad was facing down the barrel of its first league loss in front of Anfield fans since 2017.
Liverpool have only won two of their opening seven league games, falling 11 points behind league leaders Arsenal.
When Roberto Firmino scored twice each side of halftime, the Reds appeared to have reversed the tide of the game. However, Adam Webster’s own goal gave the home team the lead.
But in Roberto De Zerbi’s debut game as Brighton manager, the Seagulls earned the prize for their performance when Trossard scored seven minutes from the end.
A point drops Liverpool to ninth place, while Brighton maintains their position in fourth.
De Zerbi’s debut lived up to the expectation, as the Italian’s exquisite passing out from the back tore apart Liverpool in the first half.
Klopp defended Trent Alexander-Arnold at length when England boss Gareth Southgate disregarded him during the international break.
After only four minutes, critics of Alexander-defense Arnold’s were given additional ammo when he was twisted by Trossard and the Belgian shot into the far corner.
The nightmarish opening 20 minutes for the home team could have been considerably worse had Alisson Becker not made two crucial saves.
Danny Welbeck’s close-range header was too close to the Brazilian, who then made an outstanding save as he raced off his line to deny Trossard.
However, Liverpool were not so fortunate when they missed a third opportunity after the opening goal, as Brighton again carved an opening down Alexander-side Arnold’s and Trossard’s shot was too powerful for Alisson.
Klopp pulled Virgil van Dijk to the sideline following the second goal in an effort to restore order, and the Reds were able to gain a foothold before halftime.
A VAR review, though, saved Liverpool by halving the deficit.
Klopp had unexpectedly started the match with Luis Diaz, Diogo Jota, and Darwin Nunez on the bench, but Diaz replaced Fabio Carvalho at the start of the second half.
The Colombian had an immediate impact as he pushed the Brighton defense and crossed for Firmino, who cut inside Lewis Dunk and calmly hit the far corner.
The future of Firmino remains uncertain, as the Brazilian’s contract will expire at the conclusion of the current season.
His resurgence in front of the net should have resulted in a hat-trick, but he headed straight at Sanchez when he had the opportunity to complete the comeback.
Welbeck missed a close-range opportunity to restore Brighton’s lead as he failed to connect with a low cross.
Moments later, the Seagulls fell behind due to Sanchez’s disastrous goalkeeping blunder.
Not for the first time this season, the Spanish international fumbled a corner kick and slammed the ball into his own goal off Webster.
Brighton, in keeping with De Zerbi’s reputation as an offensive-minded coach, never ceased to press forward and finally scored when Trossard headed home Kaoru Mitsuya’s cross.