Van Dijk left Southampton in January to join Liverpool in a £75million deal.
But old habits got the better of the Dutchman as he was captured trying to enter the Saints dressing room before the match.
The 26-year-old had a sheepish look on his face as he realised his error and headed down the hallway and into the away dressing room.
But Van Dijk’s pre-game blunder had no impact on him on the field as Liverpool comfortably beat his former side.
The defender was imperious despite heavy boos from the home supporters and after the game he said the abuse was unfair.
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He said: “You just enjoy it. It’s the only thing I think you can do.
“I think it is a bit unfair because no-one really knows what happened over the summer and the last few months but I just kept my head down and enjoyed it.
“I think we should have scored more. We deserved the win but we should have made it a bit easier for ourselves.”
The result pushes Southampton into more trouble at the bottom of the league but Van Dijk is confident they can survive.
He added: “I have a lot of good friends here, I care for the club.
“It is difficult to get out of the relegation zone but they have quality players.”