Alexander-Arnold laid on the perfect assist for his Anfield team-mate as he whipped in a corner before the Barcelona defence had been allowed to set itself.
The moment of quick-thinking meant Origi was free to lash the ball in beyond the despairing grasp of Marc-Andre Ter Stegen and send Liverpool fans into pure ecstasy.
Alexander-Arnold has taken plenty of much-deserved credit for making the most of the opportunity as Barcelona’s defence switched off.
But it’s the ballboy who swiftly handed the right-back the ball to take the all-important corner that Souness wants to see rewarded.
The former Liverpool player and manager has called on his old see to hand the ballboy two season tickets, as well as tickets for next month’s Champions League final.
“Watch this. Look at the ball boy. He’s on the spot. He realises a few dopes. The great Ronnie Moran, he used to say to us: ‘find the dope,'” Souness told Virgin Media Sport.
“What he meant is at a corner kick or a throw-in or when the ball goes dead, someone would go to sleep, he would say: ‘find the dope,’ and there is a team of dopes…
“That is criminal for a professional footballer, they’ve all turned their back on it…
“Watch the ball-boy here, he puts it on the spot, watch how quickly.
“Two season tickets for this little fella, two fabulous tickets for the final for that little fella!”
Origi’s second goal of the night put Liverpool ahead for the first time in the semi-final tie as they went 4-3 up on aggregate against Barcelona.
Georginio Wijnaldum netted a brace between Origi’s goals to put Liverpool on course for a famous victory which will live long in the memory.
In overturning a 3-0 deficit from the first leg, Liverpool became the first team to do so in Champions League semi-finals history.
They will discover their Champions League final opponents this evening when Ajax take on Tottenham at the Johan Cruyff Arena.
The Amsterdam giants are 1-0 up going into tonight’s second leg fixture after Donny van de Beek bagged in north London last week.
Souness will be keenly anticipating the outcome of the showdown as Liverpool continue on the path to a potential sixth European Cup win.