Alisson was responsible for United’s equaliser during the Reds’ 3-1 victory at Anfield on Sunday, fumbling Romelu Lukaku’s cross to the feet of Jesse Lingard.
It was a rare error by the Brazilian goalkeeper, who has made a positive impact since his £65million ($81m) summer move from Roma. Indeed, with Alisson as their No.1, Liverpool have conceded just seven goals from 17 Premier League games, keeping 10 clean sheets.
Van Dijk, though, laughed that it should be 11.
Asked what he said to Alisson after the blunder, the Dutch defender said: “Why did you ruin the clean sheet?!
“I said to him, ‘We have no clean sheet because of you!’ No, I made a joke out of it. He’s been fantastic for us. It happens, everyone makes mistakes. It’s how we react and he did brilliantly in the second half. He didn’t get nervous. I said to him, ‘Just keep going, keep your head up and we’ll be fine.’”
The win over United, who have responded by sacking manager Jose Mourinho, moved Liverpool back above Manchester City to the top of the Premier League table. The Reds also sit a remarkable 19 points above United down in sixth place.
“It was obviously very important to win,” Van Dijk said. “You could say it was just another game but it was a bit special because it was against them and it’s a long time since we beat them at home. Well deserved.”
He added: “We are in mid-December and the season is still so long. We are very happy we’re in the position that we’re in now but that can change in two or three weeks so we won’t get carried away and we’ll try to keep on doing what we’re doing. Obviously, we need to stay confident.”
Next up for Jurgen Klopp’s side is a trip to Wolverhampton Wanderers on Friday. Victory at Molineux would guarantee the Reds top spot for Christmas for the first time since 2013.
“It’s another game we want to win,” said Van Dijk. “It’s going to be very tough there. They are in a great moment but so are we so we will have to prepare well and know their strengths and their weaknesses as well.”
Liverpool should have vice-captain James Milner available for Friday’s game, after the midfielder sat out the win over United due to a minor muscle issue.
“I just had a bit of a sensation in my hamstring at the end of the Napoli game,” Milner told Liverpool’s official website. “And the manager made the decision [to miss Sunday's game].
“It was the right thing not to risk me at the weekend, so hopefully I’ll be fine for the next game.”