Peru Primera: Garcilaso 3 Universitario 2
The Argentine forward struck just two minutes from time at the Estadio Municipal de Espinar to ensure Garcilaso will take a slender advantage into next Sunday's second leg in Lima.
Fredy Garcia's Garcilaso - who went into the game boasting an unbeaten home streak of 22 matches in the Primera Division - flew out of the traps and were ahead inside three minutes through Cesar Ortiz.
Victor Ferreira doubled the hosts' advantage on the stroke of half-time, before Raul Ruidiaz begun Universitario's fightback with a 68th-minute penalty.
Uruguayan striker Sebastian Fernandez looked to have earned the visitors a valuable 2-2 draw when he struck 11 minutes later.
However, Ramua had the final say to ensure 2012 runners-up Garcilaso go into the second leg in pole position to seal their maiden Primera Division title.