On 8 June 2011, Pérez signed a five-year contract with Portuguese club Benfica for a fee rumored to be around €5.5 million for his full rights from Estudiantes.

[8][9] His performances attracted attention from other clubs,[10] while Benfica manager Jorge Jesus named Pérez his side's most difficult player to replace and the "brain" of the team.

[13] At the beginning of the 2014–15 season, Pérez won the Supertaça Cândido de Oliveira, thus winning all four Portuguese titles with Benfica in the 2014 calendar year.

With no substitutes, the injured Pérez volunteered to play in goal for the entirety of the match against Colombian side Independiente Santa Fe in which River Plate won 2–1.

[24] Pérez made his Argentina senior squad debut on 30 September 2009 under then-manager Diego Maradona[25] in a friendly match against Ghana,[26] an eventual 2–0 victory for the Albicelestes.

[27] After midfielder Ángel Di María sustained an injury in the quarter-finals, Pérez started in his place in both the semi-final and final against Germany, which Argentina lost 1–0 after extra time.