But some may argue the warning signs have been there after the recent 1-0 defeat away to Atletico Madrid and the fortunate 3-2 win over West Ham on Monday. Had Jarrod Bowen taken a similar chance as Sarr did then the Hammers would have snatched at least a point at Anfield having lead 2-1.
Liverpool were also below-par in their 1-0 win over Norwich. The winter break has not proved to be a benefit to the Reds.
In most Premier League seasons every team has a bad day at the office, even a side as impressive as Liverpool. But most would not have expected that today would be the day, that they would suffer their first league defeat since January 2019 to Manchester City and by a three goal margin.
There will be disappointment no doubt at not setting a new top flight record of 19 wins on the spin and not surpassing Arsenal's Invincibles of 2003-2004 - providing some much-needed nostalgic cheer for the red half of North London after the Europa League exit this week.
But in the wider scheme of things, the Reds need just four more wins to seal their first league title in 30 years.
Klopp: You can't break records just because you want to
And maybe this humbling defeat will act as a wake-up call to knuckle down in the business end of the season having had some narrow wins in 2020.
They have had the winning habit in the league for more than a year so its is bound to be a shock to the system when they taste defeat.
Liverpool are still in the FA Cup, Champions League and are 22 points clear of Manchester City in the Premier League. Jurgen Klopp's side now have a make-or-break few weeks where they need to recover from this loss to avoid it derailing their season.
An FA Cup fifth round tie on Tuesday against Chelsea who are also keen to return to winning ways after a poor run of results. Next up in the league is Bournemouth who are fighting for their lives in the relegation battle. And then it is the second leg against Atletico at Anfield where they need to overturn a 1-0 deficit.
But having had 30 years of hurt since their last league title the priority must be sowing up the league as quickly as possible.
The most sensible thing to do is to forget about the performance at Vicarage Road. They made uncharacteristic errors in defence, playing too high a line and being second best to the ball.
Even Virgil van Dijk proved he is human after all with his defending for Watford's first two goals.
The only player who enhanced his reputation was the injured Joe Gomez who the Reds sorely missed.
Klopp admitted after the game he was surprised by the result and performance, admitting his side "weren't good enough".
Going forward the message from Klopp will no doubt be keep calm and carry on to prevent another stinging result like today.