Both teams, who contested the AFC Asian Cup UAE 2019 final which Qatar ultimately won, have shown great spirit against South America's best teams, AFP reported.
Qatar began its Group B campaign by fighting back from 2-0 down to draw 2-2 with Paraguay before a late Duvan Zapata goal denied the Asian champion a point against Colombia in its next match.
And while a youthful and inexperienced Japan side was taught a harsh lesson in clinical finishing by Chile in a 4-0 defeat, it was then on the wrong end of two VAR decisions in its 2-2 draw with Uruguay.
Both sides may only have one point from two group games so far but they know that victory in their final pool encounters will likely see them into the knockout rounds.
"We want to be protagonists on the pitch, our players have the quality to do that," said Qatar's Spanish head coach Felix Sanchez.
"We're a team that never gives up," he added about the Asian champions.
On Sunday, Qatar faces a disjointed and underwhelming Argentina for whom Lionel Messi has been unable to spark into life.
And Messi knows that a victory over Qatar, which Argentina almost certainly needs to avoid being knocked out of the competition, is anything but a foregone conclusion.
"You don't win matches any more just by pulling on the jersey," warned the Barcelona star, who turns 32 on Monday.
Having paid for its wastefulness in front of goal and naivety at the back against Chile, Japan head coach Hajime Moriyasu rang the changes ahead of its clash with Uruguay.
"They showed a lot of courage to play the game," Moriyasu said of his players, lauding their "defiant spirit" against a "top" team.
Having thrashed 10-man Ecuador 4-0 in its opener, Uruguay had to come from behind twice to snatch the draw with Japan.
Barcelona striker Luis Suarez, who equalized the first time from the controversially awarded penalty, insisted the 15-time Copa winner had not underestimated its Asian opponent.
"We knew the result against Chile the other day was unreliable," he said.
Japan came to the tournament with a squad made up mostly of under-23 players likely to be available next year for the Tokyo Olympics.
When Moriyasu announced his 23-man squad last month, 17 of the players were uncapped. Two friendlies and two Copa America matches later, and nine of those have since made their debut.
But despite fielding such inexperienced lineups, Japan has impressed with its speed and industry, as well as a willingness to attack and Ecuador can expect a test on Monday.