It was Brighton’s second penalty of the game after Neal Maupay fired a first-half spot-kick wide at the Amex Stadium.
The Reds thought they had taken the lead when Mohamed Salah latched onto a Roberto Firmino ball before firing home, but it was disallowed for offside by the video assistant referee.
Diogo Jota broke the deadlock, with his ninth goal since joining the Reds, as he received Salah’s pass before going past two defenders and firing into the bottom corner.
Substitute Sadio Mane believed he had sealed the game with a late header for Liverpool but that was also ruled out by the VAR for offside.
And they were made to pay when Andy Robertson kicked Danny Welbeck’s boot – with Stuart Attwell awarding the penalty after viewing the screen – and Gross slamming the equaliser down the centre.