Manchester City thrashed AC Milan 5-1 in a game suspended for 30 minutes because of a severe thunderstorm.
Stevan Jovetic, Scott Sinclair, Jesus Navas and Kelechi Iheanacho put City into a 4-0 lead within 26 minutes in Pittsburgh, USA.
Sulley Muntari pulled a goal back for Milan before half-time and the restart at the Heinz Field stadium was delayed because of bad weather.
Jovetic added a fifth, while Milan's Mario Balotelli had a goal disallowed.
City now face Liverpool on 30 July.
Manchester City: Caballero, Clichy, Kolarov (Richards 69), Boyata (Rekik 77), Nastasic, Fernando (Garcia 62), Zuculini (Rodwell 77), Navas (Leigh 77), Jovetic (Guidetti 69), Iheanacho (Huws 62), Sinclair.
Olympiakos 0-1 Liverpool
Raheem Sterling scored the winner as Liverpool beat Greek side Olympiakos at Soldier Field in Chicago.
Sterling latched on to a deflected shot from striker Daniel Sturridge to score from close range early in the game, while the closest Olympiakos came to an equaliser was when a Gevorg Ghazaryan effort hit the crossbar.
Reds captain Steven Gerrard started alongside Sterling, Sturridge and summer signing Lazar Markovic, who joined the club from Benfica for £20m.
Winger Markovic played the first half before being replaced by Brazilian Philippe Coutinho.
"Markovic will only get better and better," said Liverpool manager Brendan Rodgers.
"He showed great strength when he burst through and hopefully later on when he picks up that speed and sharpness in his game, he'll go on and finish that."
Liverpool: Jones, Johnson (Kelly 62), Skrtel, Toure (Coates 62), Enrique (Robinson 45), Gerrard (Leiva 62), Henderson, Can (Allen 45), Sterling (Ibe 75), Markovic (Coutinho 45), Sturridge (Lambert 74).