Kelechi Iheanacho pick-pocketed the dithering Brazilian in the penalty area before Rachid Ghezzal eventually turned the ball into the empty net.
Though the error proved inconsequential as the Reds secured a 2-1 victory, it was the first blunder committed by the £66.8 million ($86m) summer signing since his arrival from Roma.
Manager Jurgen Klopp was " really happy " with the mistake on just Alisson's fourth outing for Liverpool and Kewell sees no reason for concern ahead of the remainder of the campaign.
"The problem that Liverpool had last year was who was going to be the goalkeeper but Alisson has done excellent," the new Notts County manager told Sky Sports .
"He has made a mistake, but it's a team game and the boys stuck by him and got him through it and I'm sure he's smart enough not to make that mistake again."
Ghezzal's goal was unable to prevent Liverpool remaining top of the Premier League table as they completed a fourth win from as many games.
Klopp's side have already plundered nine goals during that period, with Roberto Firmino, Sadio Mane and last season's top scorer Mohamed Salah having already registered.
The trio netted 91 times between them last term and Kewell has sympathy for any defence faced with trying to stop Liverpool's attacking triumvirate.
"They [Salah, Mane and Firmino] are exciting and you look at the players he [Klopp] has on the bench to come on... You look at their front three: it's frightening," the ex-Australia international added.
"We always talk about Liverpool and think 'do they need that 30 goal a season striker?' But, for me, Firmino has been excellent, I can't fault him. He works so hard in positions on and off the ball which is fantastic.
"Then you have Mane and Salah driving at you at any given moment and both of them seem to have a little competition with each other to see who can score the most goals. It's just excellent."