The Toyota driver set the pace on the 1.48km asphalt stage, held in front of a bumper crowd that had congregated around the Athens harbour.
The stage was the first competitive running for WRC crews after organisers were forced to cancel the shakedown stage in host city Lamia due to the effects of Storm Daniel.
Torrential rain and thunderstorms have caused flash flooding across Greece but organisers remain confident the rally can continue safely.
Rovanpera wasted little time in getting up to speed on the rally’s opening stage, posting a time 0.3 seconds faster than nearest rival, Hyundai’s Esapekka Lappi.
“I have to hope that the conditions are better for me than they normally are in the dry,” said Rovanpera, who will start Friday’s action first on the road.
“After the disappointment in Finland, I want to do a good rally and we have to fight for it.”
Hyundai’s Thierry Neuville was third fastest, a tenth slower than his team-mate but is feeling confident about his chances.
“I haven’t felt this good for a long time in the car, so I am looking forward,” said Neuville.
“We had great speed in the last two events, that’s for sure and there is more to come.”
Source: Autosport