Paraguay won a penalty shootout 5-3 on Wednesday to reach Sunday's final, sinking a desperately unlucky Venezuelan side who had an apparent goal ruled offside and hit the woodwork three times during the goalless draw.
The match, which was marred by an ugly fight involving players and coaching staff from both sides as they left the field, ended Venezuela's remarkable run.
Long regarded as the weakest team in South America, the side known as the "vinotinto" or "red wine" for their burgundy jerseys punched above their weight to reach the Copa semi-finals for the first time.
"In my modest opinion, based on observable facts, THEY ROBBED US OF THE VICTORY GOAL! And I hope that with that I don't offend anyone," Chavez said via Twitter from Cuba where he is undergoing treatment for cancer.
"In truth, our vinotinto won last night. Paraguay did not beat us in that game. Fidel [Castro] and I saw clearly that we had a goal taken from us."
Chavez added he would complain to football's governing body in South America [CONMEBOL] about the incident.
"I think we must raise our voice because we have authority to do so before CONMEBOL," the president said on his @chavezcandanga account, which is followed by almost 1.8 million people.
"Why the devil did that referee disallow such a spectacular goal? Was one of our glorious artillery men offside? None of them!"
Paraguay will face Uruguay in the Copa final on Sunday in Buenos Aires.
The result meant Paraguay reached the final of the continent's most prestigious tournament without winning a single match in open play, having drawn three group games before beating Brazil and Venezuela in the knockout rounds on penalties.
