Joe Manganiello to Sofia Vergara -- Whoooa Oh Oh Oh ... Sweet Almost Wife O’Mine (VIDEO)

Joe Manganiello channeled his inner Axl Rose singing GnR's "Sweet Child O' Mine" and it earned him a big smooch from a groupie in the front row ... soon-to-be wife Sofia Vergara.

Sofia and Joe are tying the knot Sunday in Palm Beach and warmed up Saturday with a rager following their rehearsal dinner. They clearly were warming up their lips too because Sofia planted a giant one on Joe.

BTW ... Sofia and Joe's pre-wedding festivities outdid the average nuptials ... 2x Latin Grammy winner Jorge Celedon serenaded the crowd ... so the party Sunday should be pretty epic.