Valdez won the header from a loose ball, set up Lucas Barrios and he finished with aplomb.
Bobadilla, another substitute, carves a chance by cutting inside. Barrios is fed a through-ball, and the substitute can't believe his luck that no Argentina defenders are around him.
This Brazilian referee likes getting his cards out, particularly given we are less than 15 minutes into this tie. Sportsmail's Rik Sharma in Concepcion: Messi, Aguero and Mascherano - who will all miss the final if shown the yellow card - had better watch out.
We have our first yellow card of the fixture, and it goes to Argentina and Manchester United's Marcos Rojo for a tactical foul to break down a Paraguay counter-attack.
Perfect passing found its way to Messi, who set up Pastore with a beautiful through-ball, and the defenders just watched.
A ball over the top by Di Maria is almost inch perfect.
His first touch to control Messi's through-ball was sublime, and gave him space to find the finish. He's had an understated tournament - just scoring once - but as ever, has been the heartbeat of his team.