Paraguay coach Ramon Diaz said their pressure and half-time moves brought about Argentina's downfall in their Copa America clash on Saturday.

Coaching against his native country, Diaz masterminded Paraguay's comeback from 2-0 down to earn a 2-2 draw to snare a point from their Group B opener in La Serena.

Basel forward Derlis Gonzalez came on at half-time for Richard Ortiz, and Paraguay were more dangerous as a result - and they capitalised on the openness of the second half, via Nelson Valdez and Lucas Barrios goals.

When asked if his side were vastly different before and after the break, Diaz replied: "Yes, I agree with that. 

"I was worried about the first half because we weren't at our level. We also knew we were facing one of the best national teams in the world as Argentina are. 

"They played really well and that was the difference that time.

"After [half-time] we changed some tactical things on the pitch because of the result and we found the way, although Argentina could have scored more goals." 

Diaz said he felt Paraguay's pressure forced errors from the more-fancied Argentina, with the landlocked nation getting one-up on former coach Gerardo Martino - who led them to the Copa America final in 2011.

"We changed tactically because Argentina were better than us during the first half. 

"They are difficult to keep in control because they have [Lionel] Messi in their squad. 

"But Paraguay felt better in the second half, putting pressure on them [Argentina] even making some mistakes."

Diaz said their best was yet to come, as they look to build on their momentum when they take on Jamaica in Antofagasta on Tuesday.

"There are already many things which need to be improved sooner than later," he said. 

"It was a great result from the emotional side but we need to improve some other things, although tonight we did a difficult task, coming back from 2-0 against Argentina."