Maccarinelli's punches carried more venom early on but Afolabi was landing more cleanly and more regularly.
And a left hook to the head wobbled Afolabi in the sixth as he retreated into his shell.
The 28-year-old, who lost his WBO title to David Haye in March 2008, continues his comeback against Ola Afolabi for the interim WBO cruiserweight belt.
The fifth was arguably Maccarinelli's most successful round as a left to the body and then a three-shot combination seemed to have an impact on Afolabi.
Maccarinelli's defeat to Haye is one of two blemishes on his 29-fight record while Afolabi, also 28, has one loss and three draws in his 13-fight career.
Salzburg went close on a couple of occasions when Rabiu Afolabi headed wide from close range, while City keeper Shay Given was forced to save one-handed from Stefan Hierlander.
The Welshman stopped heavyweight Matthew Ellis in two rounds at London's ExCeL Arena last December, before suffering a shock ninth-round knock-out to Ola Afolabi in March, his third defeat in 32 fights.
Despite his questionable pedigree and punching power Afolabi punished Maccarinelli's casual defence in the ninth in the most emphatic style, when a huge overhand right came from nowhere to floor the Welshman.
And Maccarinelli is ready to take up the challenge and step out of Calzaghe's ominous shadow when he fights Afolabi on the undercard of Amir Khan's clash with Marco Antonio Barrera in Manchester.
But Afolabi spoilt his plans for unification world domination to claim the interim WBO cruiserweight belt, taken his record to 14 wins from 17 professional fights with his shock success at the MEN Arena.
The 28-year-old, a member of Calzaghe's renowned Newbridge gym, insisted he had been the "consummate professional" before the Afolabi bout after admitting to BBC Sport that he 'took things for granted' before his demolition by Haye.
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