After taking the lead in the 22nd minute via captain Sam Kerr, the Matildas conceded twice in a poor second-half display with Italy's winner coming in the final minute of injury-time.
Garriock, who played 130 times for Australia, was left frustrated by the result and questioned new coach Ante Milicic's approach.
"It's disastrous," Garriock said on Optus Sport.
"I'm so upset, more for the fact of the style we played the second half, and we touched on it at the start of the game, this high line is absolutely ridiculous.
"If you think as a coach you can come in and change the philosophy and change the style within five matches...we've just been crucified, not once, but twice.
"We've got a 15th ranked side and we're ranked 6th in the world and they've just beaten us. And if we had a better team playing against us tonight it would have been more than five.
"I'm so disappointed."
The Matildas have now lost their past three opening games at a World Cup and must pick themselves up quickly before taking on Brazil on Friday morning (AEST).
Milicic is adamant Australia can bounce back after the early set-back having reached the quarter-finals in their past three World Cup appearances.
"We have to do it the hard way, but maybe that is just the Australian way," Milicic said post-match.
"We will stare the hard way straight in the eyes and we will go for it."