The United States beat Australia 2-1 and Japan thumped Colombia 4-1 on Sunday to set up a SheBelieves Cup tournament decider on Wednesday between the two favorites.
Japan's better goal difference mean that the USA must win Wednesday's game to defend their title while Japan would be crowned with a win or a draw.
USA coach Emma Hayes changed the entire starting 11 from the team which beat Australia 4-0 in midweek but the Olympic champions got off to a perfect start.
Lynn Biyendolo (formerly Williams) opened the scoring after just 42 seconds, slotting home after Emma Sears had set up Jaedyn Shaw, whose low ball was turned home by Biyendolo for her 22nd international goal.
Biyendolo then had an effort ruled out for offside after a great run down the left from the lively Sears but the early dominance from the Americans gradually faded.
Hayes was already without many of her key starters for this tournament due to injury and not surprisingly there was little fluidity in midfield.
But the nerves eased after substitute Michelle Cooper made it 2-0 in the 68th minute after Claire Hutton's pinpoint pass had found Ally Sentnor and Cooper pounced to fire home.
It was an improved display from the Matildas, who had been outclassed by Japan in a 4-0 loss on Thursday and they earned some reward in the 80th minute when sub Michelle Haymen headed in a Hayley Raso cross.
Biyendolo said she expects a tough challenge against Japan and their stylish possession football.
"We have to show up and be ready to play and be ready to be very organized and comfortable sometimes without the ball," she said. "We will have to be very disciplined defensively and be able to transition on them."
Mina Tanaka scored a second straight brace as Japan delivered another impressive performance in defeating Colombia 4-1.
Japan took the lead in the 18th second of the game with a long-range effort from Momoko Tanikawa which flew into the top corner.
The in-form Tanaka doubled the lead in the 8th minute with a glancing header from a corner as Japan followed up their opening 4-0 win over Australia with another convincing display.
Colombia pulled a goal back just before the interval with Linda Caicedo finishing off a fluent passing move with a clinical left-foot finish.
But Japan soon restored their two goal advantage with the influential Tanaka setting up substitute Maika Hamano whose diagonal drive made it 3-1 in the 57th minute.
Tanaka added her second and Japan's fourth from the penalty spot with 10 minutes left as the Nadeshiko ensured maximum points from the opening two games in the round-robin tournament.
This is the 10th straight year of the four-team invitational competition and the USA have won all but one edition.
