In quarter-final upsets, Uruguay eliminated Lionel Messi's Argentina on penalties while Peru beat fancied Colombia 2-0 after extra-time.
"I don't want to talk about favourites, we've got it wrong every time," Uruguay's coach Oscar Tabarez said on Monday.
"Any of the four teams that are in the semi-finals have a chance of snatching the title. Paraguay, Peru and Venezuela are not going to say: 'That's it, we've got this far'," he told a news conference.
"In this tournament, [Peru] are one of the four best teams in South America. Their evolution is evident. We're going to try to mark them well, we won't go out to expose ourselves as we did in the first match. We don't believe ourselves to be superior."
Uruguay and Peru drew 1-1 in the opening match in Group C in San Juan two weeks ago, with the World Cup semi-finalists salvaging a draw after falling behind to a goal by Paolo Guerrero.
In a tournament of generally tight results, Uruguay's only victory was 1-0 against Mexico, while Peru lost to Chile and finished third in the group before upsetting Colombia 2-0 in their quarter-final in Cordoba on Saturday.
Tabarez said he would prefer to be able to attack constantly like Argentina and Brazil rather than wait for them and hit on the break.
"If we compare ourselves with Argentina they ought to rout us every time and that's not the case. We have to think about what we've got and not in what we lack," he said.
Tabarez will pit his wits against equally experienced fellow Uruguayan Sergio Markarian, at 66 two years his senior, whose work at Peru's helm has already born early fruit despite being deprived of leading players due to injuries.
Uruguay have forward Edinson Cavani still in doubt after he missed the quarter-final through injury and holding midfielder Diego Perez, who scored against Argentina but was later sent off, is suspended but centre-back Sebastian Coates returns from suspension.
In Wednesday's semi-final in Mendoza, Paraguay, who have drawn their four matches and eliminated Brazil on penalties, meet surprise package Venezuela, who had never before progressed so far.
The teams shared a thrilling 3-3 draw in their final qualifying match with two goals in the dying minutes leaving Venezuela top of their group.
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