Rumford defeated Thai teenager Phachara Khongwatmai 2&1 in the final of the £1.1million event, an innovative mixture of stroke and match play.
The 39-year-old was five shots clear of the field after the 54 holes of stroke play, although that only secured a bye in the first round of Sunday's match play stages, which were contested over six holes at Lake Karrinyup.
Rumford beat Hideto Tanihara, Wade Ormsby and Adam Bland to book his place in the final and moved in front for the second time with a birdie on the par-five fourth.
Khongwatmai, who had claimed the final berth in the match play stages after surviving an eight-man play-off for five places, then needed two attempts to escape a greenside bunker on the next and conceded Rumford's birdie putt.
Rumford won back-to-back titles in South Korea and China in 2013 but needed a medical exemption last season after an aborted 2015 campaign caused by eating an apple during the Tshwane Open which resulted in a blockage and led to 30 centimetres of his small intestine being removed.
"It's great to be back," Rumford said. "I've done a lot of reflection these past few months after missing my Tour card last year.
"I had a tough year and didn't see my family that much, only four weeks in six months. It was a gruelling six months but I'm back and I couldn't be happier.
"It's amazing to win in front of your home crowd, particularly being a new format. It's massive and I am just really proud of how hard I've worked."
Pre-tournament favourite Louis Oosthuizen had earlier birdied the sudden-death shootout hole three times in succession to finally get the better of American Johannes Veerman, but lost to Australia's Adam Bland in the quarter-finals.
Oosthuizen had a putt to win the match on the fifth hole of regulation play, but three-putted instead and missed another match-winning attempt on the second extra hole before a bogey at the third time of asking gifted Bland victory.
