Aston Villa secured Champions League qualification at Liverpool's expense - with Arne Slot's side forced to wait a top-five finish after being "taken to the cleaners" with a 4-2 loss.
Watkins' second-half double capped off a performance for Unai Emery's side - who can go into Wednesday's Europa League final with a seat at Europe's top table already in the bag.
Liverpool capitulated in the second period, with Slot's side now facing the prospect of potentially needing to beat Brentford on the final day to secure Champions League football themselves.
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"Liverpool don't excel at anything," said Jamie Carragher after a limp display. "They look like a really, really average team.
"The only time Liverpool have looked a threat is through set pieces."
Villa showed they were better than Liverpool at that as well, when Morgan Rogers curled Villa in front from a slick short corner routine just before half-time. It came in a period when Slot's side were on top but failed to take their chances.
Liverpool did find a leveller after the break when Virgil van Dijk headed home Dominik Szoboszlai's free-kick that survived a VAR check after Van Dijk and Matty Cash came together in the build-up
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But Liverpool lost all composure, despite the excellent Rio Ngumoha hitting the post just after the equaliser. Szoboszlai slipped over deep in Liverpool territory, allowing Rogers to set up Watkins for his first.
Then Villa hit top gear. Emiliano Buendia struck the inside of the post with a curling effort, but then Watkins got his second after bundling home from close range after Pau Torres' shot was saved.
The best was saved until last, with John McGinn curling home a brilliant fourth from the edge of the box.
Van Dijk pulled one back for Liverpool, but it was a disappointing night to cap off a poor campaign on the road for Liverpool this season.
There is a lot of work to be done.
More to follow...
WATCH: Four stunning goals for Aston Villa
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