Micah pulled off several impressive saves in Monday's (AEDT) SheBelieves Cup clash at State Farm Stadium in Arizona that will prompt fresh discussion over Arnold's stranglehold on the No.1 jersey.
The 27-year-old Micah was not at fault for either of America's goals - the first of which came after just 43 seconds - and her reflexes kept Australia in the game right until the final whistle.
Lynn Biyendolo put the USA ahead inside the first minute, before a dogged Australian side made the home team fight for their second goal through Michelle Cooper soon after the hour mark.
Michelle Heyman headed home a delightful Hayley Raso cross in the 80th minute to give Australia hope of salvaging a draw.
And while the Matildas could not find an equaliser, some of Micah's late glove work prevented the USA from putting the game beyond doubt.
Remarkably the outing against the USA was just Micah's 18th senior cap, with ex-Matildas coach Tony Gustavsson having opted for Arnold as his No.1.
But with Micah playing regularly with Liverpool in the Women's Super League, caretaker Australia coach Tom Sermanni says the shot-stopper is making a compelling case to become the Matildas' first-choice keeper.
"It's been close (between Arnold and Micah) for some time (and) there's been times when Teagan has actually been the number one," Sermanni said.
"The situation at the moment is Teagan has been playing week in and week out in the WSL and performing really well.
"Mackenzie hasn't played and is barely back in pre-season training (with American club side Portland).
"Particularly for a goalkeeper - it's not like an outfield player where you can run around - they need to get matches under the belt before they come in at this level."
Sermanni said it was premature to indicate which way he would go for Australia's final game of the tournament on Thursday (AEDT) against Colombia.
The coach was encouraged by the Matildas' response after he labelled their performance "un-Australian" in their opening match of the tournament, a 4-0 loss to Japan.
"Our effort and attitude were so much better in this game, especially after the start we had," Sermanni said.
"Given the performance of the last game and the result and then losing the goal after probably less than a minute, I think we could easily have just sort of caved in today.
"So from a perspective of the team digging in and sticking in there, I was really pleased with that part of our performance."
That start Sermanni referenced came in the shape of a goal for Biyendolo inside the first minute.
The Americans split the Australian defence apart with ease and Jaedyn Shaw's delivery from the left of the penalty box was easily finished by Biyendolo.
She had a second chalked off for offside five minutes later, and Micah was forced to parry away one of the American's long-range efforts.
Rocked early, the Matildas began to grow into the game as the first half wore on, then continued that rhythm after the break when they were more than a match for the world No.1.
They were, however, unable to finish their chances, and the USA had no such issues when Steph Catley and Charli Grant failed to contain Allyson Sentnor, who teed up Cooper for America's second in the 68th minute.
Heyman gave Australia hope of snatching a draw with her late strike, but all the action was at the other end, Micah doing incredibly well to deny Sentnor and keep the final score close.
31°C