The Toyota driver was one of two Rally1 entries to complete the event's attritional 15 stages without a delay, affording the Finn a comfortable winning margin of 1m31.7s over title rival and team-mate Elfyn Evans.
Rovanpera led the rally after winning Thursday night's asphalt super special in Athens but dropped to third when the rally tackled Greece's notoriously rough gravel roads.
The stages were made even more challenging thanks to torrential rain earlier in the week, courtesy of Storm Daniel, which disrupted preparations and forced organisers to cancel Thursday's shakedown.
Facing the disadvantage of starting first on the road, Rovanpera was able to limit the time loss, helped by wet and muddy conditions on Friday morning. His only scare came when he almost rolled on stage three after hitting a compression caused by the extreme weather.
The Finn headed into Saturday's much drier and traditional stages 25.5s adrift of leader Hyundai's Thierry Neuville, who headed Toyota's part-time driver Sebastien Ogier.
Neuville and Ogier were locked in a battle for the victory, with the latter briefly overhauling the Belgian on Saturday morning, before Neuville fought back to open up a 10.9s lead.
Rovanpera brought himself into the victory fight after reeling off four consecutive stage wins, before being thrust into a shock lead on Saturday afternoon when Neuville and Ogier both hit trouble.
Neuville hit a hole on stage nine, causing terminal damage to his i20 N's front-right suspension, handing the lead back to Ogier.
However, on stage 12, the final test of the afternoon loop, Ogier picked up a double rear puncture. But the collapse of his left-rear suspension moments later after an impact ultimately forced the eight-time world champion into retirement.
Source: Autosport