Having lost 3-0 at Camp Nou by a Lionel Messi-inspired Blaugrana outfit in the first leg, few were giving the Reds much, if any, hope of coming back from that defeat.
However, come back is just what they did, as Divock Origi and Georginio Wijnaldum each bagged a brace to blow Barca away and proceed to the final 4-3 on aggregate.
Much on the focus was on former Liverpool stars Suarez and Coutinho at Anfield, who cut dejected figures at the end of the game following the away side's capitulation.
However, Merson says he noticed a change in both players as soon as the seventh minute, when Origi opened the scoring for Jurgen Klopp's side.
"As soon as Liverpool got the first goal the cameras were on Luis Suarez and Philippe Coutinho - and they knew," the Arsenal legend wrote in the Daily Star. "You could see it in their eyes. They knew they were in trouble."
The Reds set the ball rolling for what has so far been a superb week for English football in Europe, with Tottenham Hotspur following them in the final after their own incredible comeback, away at Ajax on Wednesday night.
The following day, both Chelsea and Arsenal won their Europa League semi-finals, making it an unprecedented clean sweep of teams from a single nation contesting the finals of both European competitions in one season.
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