It was his in-swinging corner that led to Alisson inadvertently punching the ball into his own net after just four minutes.
Fornals whipped in the corner and Alisson, under pressure from Michail Antonio and Angelo Ogbonna, could only get a slight touch onto the ball. The ball ended up in the back of the net as the home side celebrated.
It went down as an own goal.
However, Fornals did get a goal of his own in the second half to put his side 2-1 ahead after Trent Alexander-Arnold had equalised before half-time.
Jarrod Bowen played in Fornals, who finished past Alisson to give West Ham the lead with a little more than 20 minutes remaining.
Seven minutes later, West Ham were 3-1 ahead thanks to Kurt Zouma heading in from Bowen’s corner.
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Divock Origi did pull a goal back for Liverpool but it was nothing more than a consolation.
After the match, West Ham’s two goalscorers conducted Sky Sports’ post-match interview.
They spoke about the vital victory for their side but the reporter issued the bad news that Fornals wouldn’t be awarded the opener as it went down as an Alisson own goal.
The Spaniard reacted brilliantly.
VIDEO: Fornals reacts to being told it was an own goal
“I think it’s logical. Alisson doesn’t want to kill himself,” Fornals joked.
“But doesn’t matter. It’s not Pablo Fornals goal, it’s West Ham goal and we win 3-2 so that’s the important thing.”
Alisson certainly will be wishing that Fornals is credited with the goal because the goalkeeper didn’t have a great afternoon.
He’ll feel he should have done better with all three goals that West Ham scored.
As it is, West Ham have moved ahead of Liverpool into third place in the Premier League with their victory as they continue their brilliant start to the season.