Argentina seek Americas title repeat
Ascarate, a 29-year-old who played for Pro 12 side Glasgow Warriors in 2013 and 2014, is among eight changes for the South Americans as they bid to retain the crown in the Six Nations-style event.
Ascarate will start at full-back for Saturday's clash in the city of Comodoro Rivadavia.
Among others earning a call-up into the Argentina starting XV are inside centre Bruno Devoto, wing Julian Dominguez, flanker Francisco Gorrissen and prop Francisco Ferronato.
"It will be a very physical game, very hard, but if we perform our game plan well and we utilize our speed, it will go very well," Argentina replacement prop Franco Brarda said.
Scrum-half Sebastian Cancelliere, who shares the tournament lead with five tries, will spearhead an Argentine attack which so far has been the most potent in the competition, with a 166-point scoring difference.
The USA Eagles, led by four tries each from Tony Lamborn and Mike Te'o, are also 4-0 but trail in scoring difference by 47 points, a factor that could decide the title if the clubs draw as they did last year in Houston, Texas, in a game that finished 35-35.
Canada (1-3) will visit Brazil (1-3) on Friday and Uruguay (2-2) will play host to Chile (0-4) in the other closing matches of the six-team event.
For Canada and the US squad, the matches serve as a tuneup for their Rugby World Cup qualifying series in June.