Alisson was celebrated after their win at PSG in the Champions League, but Slot says yesterday's performance was superior.
Discussing senior trio Virgil van Dijk, Mohamed Salah and Alisson, the Dutchman said afterwards: "Very important.
"It would not be completely fair to only talk about them but I think as a manager what you're looking for is always the ones that have achieved already a lot of things in their careers, that they step up in the most important moments of the season. I think it is always in the end of the season moments are getting bigger and bigger, and today all three of them showed up – not only these three but you're asking me about these three – in big moments.
"Alisson probably had his best game of the season today and Virgil scored the header that got us three points. And Mo was, again, very important in the first goal and he was really lively in the first half, so I saw the Mo Salah again from most parts of the season.
"Definitely credit to West Ham as well but you don't only see this here – I see this every game that I watch. I don't watch every game of the Premier League but the ones I do, I thought yesterday after 20 minutes that Crystal Palace were in a good place and they could have scored the 3-0 which was fractionally offside and they lost 5-2. So, these are the margins that are in the Premier League, which makes it such a hard league to play in but also why it's so popular."
The win sees Liverpool qualify for next season's Champions League and Slot also said, "I think it is the main aim for the club because they have experienced two years ago how much of an impact it is if you are not a part of the Champions League. So, yes indeed.
"The main aim in what they told me is look at the players, give your opinion about it so we can go into this project in the second and the third year, but do qualify for the Champions League. We all know that even the team who is in 16th at the moment has very good players, but the top eight all have incredible players."