The biggest story in world football since the most recent Champions League final (May, 2019) … was Liverpool’s dominance of European soccer.

Before their game at Watford last night, Liverpool not only was being called “the best club football team in the world”, and they had some staggering numbers to back up that assessment.

Unbeaten in 44 Premier League matches reaching back to the first week of January. Last January.

Victors in 18 consecutive Premier League matches, leaving them tied with last year’s Manchester City side for the longest streak in a century-plus of top-flight history.

And, of course, the Champions League victory over Tottenham last May, with Barcelona and Messi having been beaten, en route.

Liverpool matches became must-see TV all over the world. How far would the Reds take this.

The notion that they would have any trouble last night was really hard to get behind, given their opponent:

Struggling Watford, 19th in the 20-team PL standings, at dire risk for demotion to the second tier.

All of which led to a shocking result:

Watford 3, Liverpool 0 — the first Premier League defeat for Liverpool since January 3 — 423 days previous.

You could knock over the world football cognoscenti with a feather, and it wouldn’t need to be a big one.

It made for riveting viewing.

Something about Liverpool seemed a little off, and it was obvious from kickoff. Maybe it was Leap Year Day fixture that discombobulated them.

They seemed tired, even jaded, lacking spark to press forward. But this is the team of Mohamed Salah, Sadio Mane, Roberto Firmino, Virgil van Dijk and the goalkeeper Alisson. They might not finish the season unbeaten in the league, but they ought to win this match without pushing too hard.

Or would they?

Watford seemed genuinely feisty in beating Liverpool to balls and charging into the attacking end. They weren’t hunkering down, anticipating the beating we thought was coming.

But … but …

Watford looked like a real threat to score. Few of us expected that. Especially when their most impressive player in the first half-hour, midfielder Gerard Deulofeu, went down with an ugly looking knee injury.

It was scoreless at halftime, but pretty much everyone watching the match must have figured Liverpool coach Jurgen Klopp would slap around his stars, and they would tune in long enough to hang another defeat on Watford.

Then came the second half, and the ground under our feet shifted.

For starters, if Klopp had given any pep talk, it fell on deaf ears. Liverpool’s stars still looked as if they were sleep-walking. They looked like a team playing its fourth match in 15 days, three of them on the road, one a 1-0 first-leg loss to Atletico Madrid in the Champions League round of 16.

The attacking threesome looked disinterested. Sane was particularly moonstruck. It didn’t help the Reds’ cause that Klopp inexplicably chose serial gaffe-meister Dejan Luvren to play fullback, and he was awful, as he often is, and Fabinho, slotted in at midfield ahead of Jordan Henderson or James Milner, was hardly better.

Then Watford scored! Ismaila Sarr, in the 54th minute, Watford’s $25 million club-record purchase in hopes of getting enough goals from him to stay in the Premier League.

Watford fans were jumping in the aisles when the ball went in, but surely this act of cheek would shake awake Liverpool. Fifteen minutes ought to see them tied and then ahead.

Instead, Watford poured it on. Sarr caught Liverpool’s defense loitering near the touch line, 40 yards from goal, and a pass from Troy Deeney set him off, beating Alisson from 15 yards.

2-0? 2-0!

Sarr, a 22-year-old striker from Senegal, almost picked up a third goal, but instead put a perfect pass over to Deeney, who banged it home in the 72nd minute.

Liverpool was done. Watford exulted in victory.

Liverpool lead the league by a staggering 22 points, and ought to clinch their first Premier League title before the end of March.

Meantime, I loved tonight’s game.

One of the usually accurate perceptions of the Premier League is that anybody can beat anybody. That is why I spend so much time watching it.

Norwich defeated Manchester City this season. Watford took down mighty Liverpool.

Second, I am an Arsenal fan, and I have been using my tiny bit of cosmic energy to will Liverpool to defeat. Why? Because Arsenal holds the league record for longest streak without defeat, at 49, and Liverpool just fell five short.

Third, Liverpool fans were banking on an unbeaten season, which only Arsenal has managed, back in 2004-05, a team known as The Invincibles — and I didn’t want the Gunners to share that name with Liverpool.

Liverpool can have the league. It’s about time, really. Nothing since 1990? Blackburn Rovers and Leicester have won since then. Go ahead, Klopp & Co.

But it won’t be with an unbeaten season. Ha.

Thanks, Watford.