Leaney, who only dropped one shot over the 72 holes in Pulheim, produced another faultless display for a five-under par 67 and a 22-under total of 266 for the tournament.

Victory at the $3m event was the biggest win of the Australian's career.

The 33-year-old had started the final round two strokes behind Casey and level in second place with Germany's Alex Cejka.

But Casey endured mixed fortunes on the course for a round of 71 to finish level in third with Nick Dougherty and Ian Woosnam.

Leaney's closest threat came from Cjeka, but four birdies on the front nine put him in a commanding position.

He initially took the lead with birdies on the seventh and eighth holes.

And he wrapped up the win with a six-inch par putt on the 18th, while Cjeka's par was enough for second overall.

Leaney collected $498,000 for the win and gained a five-year exemption on the European Tour, which had been due to expire in a few months.

Among the other leading contenders Colin Montgomerie was ninth overall, six strokes behind Leaney.

Ryder Cup team-mate Thomas Bjorn was 16th at 12-under and Open champion Ernie Els was 23rd, a stroke further back.