Rooney for the first time in Tuesday’s Champions League win over CFR Cluj.
Sir Alex explained that he opted for the duo in an intriguing three-pronged forward line that also featured Javier Hernandez to combat Cluj’s threat on the counter-attack.
"For the last couple of years, Wayne has played a lot in behind one striker," he said. "But Cluj are a useful side who rely on the counter-attack, so we tried to avoid that as much as we could.
"In fact, their goal was from a counter-attack, but we tried to force them onto us so we could counter-attack ourselves.
"Chicharito was occupying the main two central defenders so we’d have a wee bit more space for Rooney and van Persie."