Defending champions Chile will play Mexico in the next round on Saturday, with Argentina facing Venezuela the same day.
Vargas says: “This was important for me and for the team. It has boosted our confidence for the games to come.
“We are Copa America champions but we haven’t played as well as we did in the last Copa America and this will give us confidence.”
In Seattle, few were expecting anything other than an Argentine win over already-eliminated Bolivia and most of the attention was focused on whether Lionel Messi would surpass Gabriel Batistuta’s record of 54 goals for his country.
Needing one to tie the mark, Messi came on as a second-half substitute with his team already 3-0 up through Erik Lamela, Ezequiel Lavezzi and Victor Cuesta and only came close to scoring with a free-kick.
USA met Ecuador in the first quarterfinal last night.
Copa America Quarterfinals
Tomorrow: Peru v Colombia (2am)
Sunday: Argentina v Venezuela (1am), Mexico v Chile (4am)