However, the Randers FC stopper made the save to condemn the Barcelona playmaker to his first ever missed penalty for Argentina, as well as a share of the spoils for the Icelanders.
"For me as a goalkeeper to play for Iceland and face the best player in the world at a penalty is a big moment and a dream come true to save it," Halldorsson told BBC Sport.
"Especially as it helped us get a big point which I hope is going to prove important to us. It is our goal to qualify.
"I did some homework. This was a situation which I knew could come up. I looked at a lot of penalties from Messi and had a good feeling that he would go this way today."
Messi has missed four of the last seven spot kicks that he has taken for club and country, not including penalty shootouts.