Juan Pablo Mirenda, the Argentinian flanker, scored his side's first try after a spectacular break by outside centre Francisco Cuneo, who ran from the halfway line only to be stopped 10 metres short of the line.
Wales came back with a try of their own through lock, William Rhys Jones, displaying an impressive sidestep to beat the last defender. The half time score was 15-13 to Wales.
Wales put on an outstanding display in terms of lineout work throughout the game. A strong lineout drive five metres out from the Argentinian line saw prop Craig Mitchell crashing over the line. A penalty try and a try scored by replacement player, Aaron Bramwell, put the game out of reach for Argentina who found it very difficult getting the ball in the Welsh half.
Summing up his team's performance, Wales coach Ian Jones said: "In the first half we weren't getting quick ball. This changed in the second half and allowed us to get more points."
Wales Captain Jonathan Spratt was pleased with the overall performance but saw room for improvement in the U19s final game: "We defended well and I think we can work on our general play for the next game."
To Argentina's credit, they kept on trying, and Cuneo ran 60 metres to score a well deserved try.
Tries: Jamie Huw Roberts (1)
William Rhys Jones (1)
Craig Mitchell (1)
Penalty try: (1) Aaron Bramwell
Penalties: Martin Roberts (1)
Conversions: Martin Roberts (4)
Tries: Juan Pablo Mirenda (1)
Francisco Cuneo (1)
Penalties: Benjamin Urdapilleta (2)
Conversions: Benjamin Urdapilleta (1)