Liverpool, for the first time in some while, enter the final week of the season involved in both the Champions League and Premier League shake-up.
However, the forces of footballing gods have moved against Liverpool at this critical juncture and the reds now need nothing short of a miracle in both this game and the weekend's set of results.
The reds were more than competent in the Camp Nou last Wednesday - going behind shortly after Naby Keita suffered a first half injury which required a first half substitution.
Mane then missed a glorious chance to equalise, as did a host of other reds.
Then, on the counter, the reds suffered a second goal sucker-punch before Messi slammed in an amazing free kick that had debatable circumstances in its award.
Rhian Brewster could make his debut in this game.
Strap yourself in.
As it happened...
In all European competition, Liverpool have only lost one of their 18 home semi-finals at Anfield (W14 D3 L1).
That was against Leeds in the old Fairs Cup back in 1971.
The bookmakers currently have Barcelona at 1/33 to reach the final. In other words they would reward you risking every £1 by giving you 3 pennies.
The Catalan club start as huge favourites and it's understandable. Roma did manage to overturn a 3 goal first leg deficit last season - however they did have a crucial away goal at the Nou Camp. Liverpool do not even have that luxury,
Do Liverpool play the patient game or go gung ho and risk an early Barcelona goal that will end the contest?
Barcelona keep the same starting XI from last weeks 3-0 win.
They rested all 11 players at the weekend.
Shaqiri and Origi named in the side as Salah and Firmino replacements. Oxlade-Chamberlain has a slight muscle strain and wasn't risked.
Alisson, Alexander-Arnold, Matip, Van Dijk, Robertson, Fabinho, Milner, Henderson, Mane, Shaqiri, Origi.
Subs: Mignolet, Wijnaldum, Lovren, Gomez, Sturridge, Brewster, Woodburn.
It's an identical Barcelona starting XI to last weeks game.
And there's only one change on the subs bench with Thomas Vermaelen replacing Dembele.
He's arrived at Anfield.
He walks around the perimeter of the pitch and down the tunnel with a T-shirt emblazoned with the message 'Never Give Up'.
Klopp last night:
Two of the World's best strikers are not available and we have to score 4 goals to go through against Barcelona in 90 minutes.
That doesn't make it easy.
We've got one back.
Huge task still ahead but LFC have played well again.
LFC 1-0 Barcelona
Robertson replaced by Gini at half time.
51' van Dijk goes close. Beaten off the line.
Wijnaldum drills it in. Hello indeed!
57' WIJNALDUM! Holy shit. Its level.
Yellow for Matip.
Messi over the free kick.
Origi. Unbelievable goal from a corner.
Were in front!
85' origi off for gomez
90 Sturridge on. Shaqiri off.
5 mins added time.
We've not calmed down yet.
The greatest result at Anfield.
Going to struggle to sleep tonight.
Madrid. June 1st.