The J.League champions dominated throughout at Yokohama International Stadium although they spurned several chances before a spectacular long-range strike from Aoyama sent New Zealand outfit Auckland City out of the tournament.
Sanfrecce will next take on African champions Al Ahly on Sunday.
The host representatives were backed to the rafters at the site of the 2002 World Cup final and they started well, with some good build-up play ending with goalkeeper Tamati Williams producing a fine stop to deny Aoyama.
The Auckland keeper was nearly beaten direct from a corner taken by Yojiro Takahagi but it came off the post with Koji Morisaki's follow-up parried away by Williams.
The pattern continued into the second half and Takahagi once again could only find the woodwork with his strike from distance while Williams kept his goal intact after Morisaki had risen well at the back post from Mihael Mikic's right-wing cross.
Hiroshima were finally rewarded in the 66th minute when Aoyama spectacularly fired into the top corner from 25 yards - a worthy way to mark the 200th goal in Club World Cup history.
The Japanese side could not find a second goal to kill the game off although they comfortably held on in the closing stages.