Veteran striker Girelli, 33, replaced 16-year-old midfielder Giulia Dragoni in the 83rd minute and needed only four minutes to make an impact, beating goalkeeper Vanina Correa with a fine header to seal a hard-fought victory.
Italy plays Sweden in Wellington on Saturday. The two teams are level on points but Sweden holds a slender advantage in Group G, topping the group on number of goals scored thanks to their 2-1 win over South Africa on Sunday.
“When you have a player like Cristiana Girelli on the bench and you see that you can’t actually score … my choice was very simple,” Italy coach Milena Bertolini said.
“She’s a weapon for us. We had a lot of the ball but just couldn’t get it into the net. And so having a player like her on the bench, it’s natural that you ask her to take to the pitch.”
Italy’s Ariana Caruso and Valentina Giacinti both had goals ruled offside in a competitive first half after Argentina nearly made a sensational start to the game, when Mariana Larroquette’s bicycle kick went narrowly wide in the second minute.
After a slow start to the second half, Italy settled into their rhythm and looked more likely to score. Manuela Giuliano’s free kick drifted over the crossbar before Giadda Greggi drew a smart stop from Correa in the 82nd minute.
Goalkeeper Francesca Durante pushed away Argentine midfielder Florencia Bonsegundo’s attempt from a free kick in stoppage time, ensuring a winning start in the tournament for the 2019 quarter-finalists in front of a crowd of 30,889.
Bertolini was vindicated after putting her faith in Dragoni as the teenager impressed on her debut before making way for Girelli, the oldest member of Italy’s squad, who scored her 54th international goal on her 104th appearance.
“Giulia is a talent,” Bertolini said. “She was ready both technically and tactically. I think that she did very well considering her age and also playing in such a big stadium in such a big event.”
Argentina caused plenty of problems for Durante but could not manage a shot on target until Bonsegundo’s free kick in the 94th minute.
They next face South Africa on Friday in Dunedin, with both teams still searching for a first World Cup victory.
“It was a very even match,” Argentina coach German Portanova said. “At times we controlled it and they did not have many opportunities. The result was somewhat unfair. A draw would have been the right score.”