Jurgen Klopp moved to snap up the Brazil international during the summer of 2018.
With Simon Mignolet and Loris Karius having failed to convince between the sticks, the Reds invested heavily in an effort to fill a problematic position.
Alisson has delivered an immediate return on that show of faith, with the Reds having sustained a challenge for the English top-flight title while also reaching the Champions League final.
A reliable last line of defence has aided their cause considerably, but a 26-year-old custodian is yet to reach his peak and can get even better in the years to come.
Achterberg, Liverpool’s goalkeeping coach, told the club’s official website: “When you come new into the Premier League, you always need time to settle in, but he picked it up quickly.
“There were a couple of areas where he needed to adapt, but everything else was automatic. We worked in training on the things that could happen in terms of aggression, players trying to block and things like that, so I think he was well prepared.
“If you have a season like he’s just had – and we still have one game to go – it’ll be hard to beat. 21 league clean sheets! He had a great season and his level was probably one of the best in the world, so we cannot complain.
“In the Champions League, he made some massive saves for us – the Napoli save for us to get qualification for the next stage – and then in the Barca game, you cannot make any errors and he made some match-winning saves to get us the clean sheet we needed.
“Hopefully next year we can improve even further; there are always small things we can be better on. We’ve spoken to Ali about them and hopefully he can improve even further for next season. Our aim is to do it again.”
Achterberg added: “He is really calm under pressure and makes good decisions.
“The calmness he gives to the team, the decision-making, that is vital for any goalkeeper.
“He is always able to make a match-winning save and make the team steady in front of him, knowing if anything goes wrong he will be there. You have to be in every moment 100 per cent focused and make the right decisions – that’s what he has been doing consistently for most of the season. That’s the level he produced – and now we need to try to make that even better.”
Alisson conceded just 22 goals across 38 appearances in the 2018-19 Premier League season, with his performances ensuring that back-up keeper Mignolet barely got a look in.
“Simon has been for a long period a No.1 goalkeeper, so it’s not an easy situation for him,” Achterberg added on a Belgium international who may look for a move this summer.
“You always want to play; you always have to find the motivation and drive to keep going and wait for the moment you’re needed. He has been unbelievable in that way.
“He has been training day in, day out to the highest level, in the gym doing everything perfectly – the perfect lifestyle and perfect professional. He has given a good example to all the young ‘keepers at the club and it’s really important he is part of the team as well. Si has a good level, of course, and I can be only positive about him.”