Alisson wandered into the opposing penalty box at the Hawthorns more in hope than expectation last term before heading home a season-defining goal for Liverpool.
The Reds, who battled through last season despite a plethora of injuries, were mounting a late charge as they aimed to get into the top four and this season's Champions League.
West Brom, who suffered relegation, were looking to steal a point off Liverpool for the second time in the season.
Hal Robson-Kanu opened the scoring before Mo Salah equalised. Then Alisson's winner came in the 96th minute and saw him mobbed by his teammates in the empty stadium.
The Brazilian had lost his father three months earlier but was determined to help the Merseyside outfit get back into the Champions League, having previously tasted success in the competition.
As he fought back tears in front of the TV cameras after the match, he said: “I’m too emotional because of these last months and everything that happened with me and my family, but football is my life and I’ve played since I remember as a human being with my father. I hope he was here to see it but I’m sure that he has seen it with God on his side and celebrating.
“It’s for my family, for the boys, what a fight.
"Sometimes we are fighting and fighting and things are just not happening. Just scoring this goal, I am really happy to help them because they fight a lot, we fight a lot together and we have a strong goal to achieve the Champions League because we won it once and everything starts with qualification. I can’t be more happy than I am now.”
Had it not been for that goal by the rarest of goalscorers then the Reds may not have been playing in Europe's top competition. After the win at the Baggies the Reds remained fifth, one point off Chelsea and three behind Leicester. They won their final two games to seal third place.
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This term they've peaked just at the right time and remain on the cusp of the quadruple.
The Carabao Cup is secured and they went one step closer to the historic feat by beating Villarreal in the semi-finals of the Champions League. Inter Milan and Benfica have also been seen off in the knockout stages.
Now either Manchester City or Real Madrid will stand between them and a second European triumph in four seasons.
Jurgen Klopp claim he has no preference when it comes to an opponent.
He said: "It’s not like I would wish for one or the other, it will be massive. And whoever wins tomorrow night or gets the result will deserve it and then we will face each other in Paris."
