"I saw the ball in the net and didn't know who had taken the corner, it was too quick for me," enthused Jurgen Klopp . "Oh my God – genius."
The Premier League side produced a comeback to rival their famous Champions League final win over AC Milan in Istanbul back in 2005 to overturn the Catalan side, who arrived at Anfield boasting a 3-0 lead.
With less than an hour played on Merseyside, Liverpool had somehow clawed their way back into the tie, with goals from Origi and Georginio Wijnaldum rendering Barca's earlier advantage obsolete.
And the decisive moment came in the 79th minute as Alexander-Arnold's quickly-taken corner kick reached Origi, who smashed beyond Marc-Andre ter Stegen to make it 4-3 on aggregate .
Lionel Messi, Gerard Pique and Co. were left stunned. Luis Suarez issued an apology to the fans and admitted that the fourth goal made Barca look like a team of children.
Was Trent Alexander-Arnold's corner kick vs Barcelona legal?
Some people - those Barcelona fans who are still in disbelief, perhaps - may be wondering whether or not Alexander-Arnold's corner kick was legal.
The short answer to that question is yes. You can see the procedure for taking corner kicks from the Laws of the Game below.
Law 17 - Corner Kick Procedure
- The ball must be placed in the corner area nearest to the point where the ball passed over the goal line.
- The ball must be stationary and is kicked by a player of the attacking team.
- The ball is in play when it is kicked and clearly moves; it does not need to leave the corner area.
- The corner flagpost must not be moved.
- Opponents must remain at least 9.15 m (10 yds) from the corner arc until the ball is in play.
As you can see, there is nothing written into the rules that necessitates the player to wait for the referee's whistle or signal before taking the corner.
SIMPLY GENIUS 🤯— Football on BT Sport (@btsportfootball) May 7, 2019
Trent Alexander-Arnold spots Barcelona napping and Divock Origi makes no mistake!!!
4-0 Liverpool 😱
The only time a corner kick is rendered illegal is if the kicker touches the ball twice (i.e. before it has reached another player), handles the ball or kicks the ball at an opponent in a reckless manner, using excessive force, in order to play the ball again.
"It was just one of those moments where you see the opportunity," explained Alexander-Arnold afterwards.
"Divock was switched on and finished it off. It probably came at him a bit fast but he is a top player.
"He scored two goals for us tonight and everyone will remember this moment."
It's not the first time a footballer has taken advantage of his opponents losing their concentration during a dead-ball scenario and it won't be the last.