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.
‘I’ll never say never to managing my country, but I’m really happy now. As long as they’re not competing against the USA, I’ll always cheer on the Lionesses’: Emma Hayes on career future
‘Scoring five goals in nine minutes is an epic thing. Someone cleared another chance off the line and I was a bit angry afterwards – I could have had six!’: Robert Lewandowski bemoans failing to hit double hat-trick while at Bayern Munich
