After O'Reilly (4/27) helped Lions restrict the Caribbean side to 148 for nine, Petersen (57) and Cameron (78) shared a 75-ball 133-run second wicket unbeaten stand to help the South African side overwhelm the target with more than four overs to spare.
Steven Jacobs was the lone bright spot in Guyana's batting chart with a 37-ball 34, while skipper Ramnaresh Sarwan (21) was the other notable run-getter.
Chasing a modest 149, Cameron returned to form in style with a quickfire 78 that came off just 42 deliveries, while Petersen also blossomed in the right-hander's company to score a breezy 38-ball 57 to take Lions home at the New Wanderers stadium here.
Text: PTI
Images: AFP
In Image: Guyana's Jonathan Foo is clean bowled by Highveld Lions' Ethan O'Reilly during the Champions League Twenty20 League match between Guyana and Highveld Lions at Wanderers stadium in Johannesburg on September 19, 2010