Brighton dumped FA Cup holders Liverpool out of the competition on Sunday as Hollywood star and Wrexham co-owner Ryan Reynolds saw his non-league side denied a dramatic win by Sheffield United in a six-goal thriller.Kaoru Mitoma's brilliant control and finish in stoppage time to seal a 2-1 win for Brighton was another enormous blow to Liverpool, whose season is unravelling just months after they came close to winning a historic quadruple.The Reds had led at the Amex through Harvey Elliott, but have now won just once in their past six games in all competitions.Lewis Dunk levelled before the break for the home side and they were well worth their place in the fifth round courtesy of a moment of magic from Mitoma.The Japanese winger cushioned Pervis Estupinan's cross into his path, flicked the ball over Joe Gomez and fired high past Alisson Becker in the 92nd minute."He is an incredible player who I think can play one step higher," said Brighton boss Roberto De Zerbi. "I am pleased for his goal."Liverpool are languishing in ninth place in the Premier League, 21 points behind pacesetters Arsenal.An FA Cup exit at the fourth-round stage leaves the Champions League as their only remaining shot at a trophy this season.Jurgen Klopp described Brighton's 3-0 win when the sides met earlier this month as a "horror show".And the German coach at least took some heart from his team's battling performance on Sunday."I am not over the moon about this performance but, again, the only thing that happened really is that we lost against a good side, who we lost to two weeks ago in a horrendous game," said Klopp. "Today was much better."We are obviously in a situation where we constantly want to make the final step.