The German timed his leap perfectly while still on the run and made firm contact with his right foot while almost upside-down to put the ball into the top corner.
The Brazil global, who had scored four goals in his five previous league games, appeared to sustain a dead leg in an early collision with Adrian Mariappa at Vicarage Road.
As is the case in nearly every post-match interview with Jurgen Klopp following a win, the Anfield boss was all smiles and took the time to appreciate (via Sky Sports) what was a Goal of the Season contender from his number 23.
"It was the best goal I've ever scored".
'I didn't think too much, to be honest, ' he added.
Victory kept Liverpool in third place in the table but in terms of Champions League qualification it pushed them four points clear of fifth-placed Manchester United, who have a game in hand.
Southampton pose as perhaps our most hard test out of the final three league games still to be played and it is important Klopp has Coutinho at his disposal. We accepted that a lot had to change in that type of game.More news: Aisha Buhari meets 82 Chibok school girls in Abuja
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"Everything is in our hands".
"I thought we improved from last week when we didn't look patient enough, but today we looked better and had these moments - of course, we didn't train for a bicycle kick from Emre!" Yes, he is a good boy, he helps us.
Klopp, however, said he needed to see his goal again to fully appreciate the moment.
Having lost Coutinho to injury early in the game, the Reds were wasteful in attack, although Watford goalkeeper Heurelho Gomes also deserves credit for keeping the Reds at bay. I think it was probably a dead leg. "We didn't play perfectly tonight but conceding in the last second would not have been deserved". It's the laugh that gets me every time. "I was a bit exhausted at the end, but I've had five or six weeks out of the game so that's only normal".
"They are a difficult-to-play-against opponent, deep defending", he said of Watford.
"Aside from the crossbar from Prodl, there were two mistakes from the referee, offsides against Okaka and Deeney, so I think we played a good game. It's a tough one but those are the margins at this level".