Jamie Carragher: 'Alisson's impact has been the biggest factor in turning Liverpool into title challengers'
A great goalkeeper is no guarantee of winning major trophies, but not having one is a guarantee you will fall short when it matters.
Liverpool realised that to great cost on and off the pitch in the Champions League final last May. It was a major statement when they paid Roma £65m - a world record at the time - for Alisson Becker. No one is querying that fee now.
"I would have paid double if I had known how good he is," Jurgen Klopp told me immediately after Liverpool's win over Napoli last Tuesday night.
Klopp is reaping the rewards of signing a goalkeeper with the potential to become the world's best. When was the last time an Anfield keeper was staking such a claim?
For the last three years this title has been David De Gea's. The performance he gave away at Arsenal last season was the best I have ever seen from a goalkeeper.
Without De Gea, Manchester United's decline since the retirement of Alex Ferguson would be steeper, yet he arrives at Anfield tomorrow with his position as the Premier League number one under threat, not just because of Alisson's form, but the Spanish goalkeeper's dip.
United look as though they will miss out on Champions League qualification in 2019. One of the reasons they are already fighting to stay in contention is De Gea has not been playing to the same high standard. He was getting his underperforming team out of trouble, but that is not happening now.
The statistics make alarming reading for United fans. Last season De Gea conceded 28 goals to help United finished second. He has been beaten 26 times already in this campaign.
His shot-to-save ratio put him at number one with 80.3pc a year ago. Now he is 11th, on 67.5pc.
Contrast this with Alisson, who is topping the charts with his save ratio and has 10 clean sheets in 16 matches.
In games against Everton, Burnley and, most spectacularly, Napoli, Alisson produced the kind of save we have come accustomed to seeing from De Gea. It was the timing that made them so good - invaluable contributions at huge moments.
There have been some excellent goalkeepers at Liverpool during the last 30 years, Pepe Reina being the best I played with. He won the Premier League's 'Golden Glove' for the most clean sheets in three successive seasons and was an essential part of a strong defence under Rafa Benitez.
But in the era of Petr Cech and Edwin van der Sar, we never claimed to have the league's best. We never had a goalkeeper our rivals wished they had signed.
It is a cliche when discussing teams capable of winning the Premier League to acclaim 'the final piece of the jigsaw', but whether Liverpool stay ahead of Manchester City or not, Alisson has taken them to the next level - his performances already worth at least six points. Probably more.
These are the contributions those who regularly compete for the Premier League take for granted. Show me a Premier League-winning team and I will direct you towards the goalkeeper who turned draws into wins and defeats into draws.
Ask Manchester United supporters to name the most important signing of the Ferguson era and the most likely response is Eric Cantona, who joined from Leeds United in 1992. I disagree.
I have always believed the seeds of Ferguson's glorious reign were planted a year earlier when Peter Schmeichel arrived from Denmark. Schmeichel made the biggest difference overall, keeping 22 clean sheets in the season United ended their title drought.
Gary Neville once told in me he felt he played with only two genuinely world class players in his Manchester United career. One was Cristiano Ronaldo. The other was Schmeichel. That is how fundamental he was to United's success.
United endured a shorter wait for the title between 2003 and 2007. What changed? The signing of Van Der Sar from Fulham. He won four Premier League titles at Old Trafford, bringing assurance to a position that had been a problem since Schmeichel's exit.
Other clubs can testify to the transformative impact of a class goalkeeper. Ederson massively improved Manchester City at the start of last season - they would not have won 100 points with Claudio Bravo. The confidence across the side grew as the season progressed because they signed a goalkeeper as good with his hands as his feet.
Cech was one of Jose Mourinho's 'untouchables' after his arrival at Chelsea in the summer of 2004.
How many titles have Arsenal won since David Seaman left? One. Arsene Wenger never really found another so good, although Jens Lehmann performed when 'The Invincibles' stormed to the title in 2003/04.
Go further back and one of my childhood heroes was Everton's Neville Southall, who was one of the greatest goalkeepers of his generation.
I used to stand behind Southall on the Gwladys Street in the mid-1980s, watching in awe at some one of the saves he made.
It is too early to claim that Liverpool have a number one of similar stature to these greats, but the signs are good.
For Liverpool to stay above City, Klopp had to eradicate every weakness in his line-up. He did that at centre-half when signing Virgil Van Dijk, but the Champions League final against Real Madrid brutally underlined it does not matter how brilliant the rest of your starting XI; an unreliable goalkeeper will always get found out the highest level - particularly over the course of 38 mentally demanding Premier League games.
In Alisson, Liverpool may have recruited their De Gea. If they win the title, they will have their Schmeichel. (© Daily Telegraph, London.)