The Scandinavian side won 1-0 in Nizhny Novgorod thanks to captain Andreas Granqvist's spot kick in the 65th minute, joining Mexico at the top of Group F.
Referee Joel Aguilar initially dismissed the players' vehement demands for a penalty after Kim Min-woo fouled Viktor Claesson but after consulting the video he changed his mind.
“I think there was no doubt about this penalty, it should have been called straight away,” said Andersson. “I think it's a very, very clear penalty.”
The time from the foul to the goal was three minutes. It was the third VAR (Video Assistant Referee) penalty awarded at the World Cup so far after France and Peru also benefited from video referrals.
Sweden's win was fully deserved against a disappointing South Korea side who are a pale shadow of the team that reached the semi-finals in 2002.
But their lack of sharpness in front of goal in the post-Zlatan Ibrahimovic era resurfaced in Nizhny.
The best three chances fell to Marcus Berg but he was denied by a combination of good goalkeeping, last-ditch defending and uncertainty in front of goal.
Andersson said he was not worried by another largely toothless Swedish display, saying he believed the goals would come.
“Anyone who has seen Marcus Berg play knows he will score all three chances next time around,” he said.
The win was reward for Sweden's more attacking approach but it was unsurprising the winner came from the penalty spot in a game between two sides who had struggled for goals in the run-up to the tournament.
Sweden never really convinced that they would score prior to the penalty despite their domination and South Korea did not manage one shot on target in the entire game.
They should have equalised in the dying seconds but Hwang Hee-chan put a free header wide, spurning the Koreans' best chance.