Victory looked all but guaranteed for Suninen, who was making his first start of the season with a Hyundai Motorsport-prepared i20 N Rally2.
The Finn headed Rossel by over half a minute at the start of the final day and claimed a brace of fastest times on Sunday’s opening tests to stretch his lead even further.
Suninen had a huge 57.1sec in hand over the Frenchman before the Wolf Power Stage, but his dreams were shattered by a crash just a few hundred metres into the finale.
With his rival’s car stuck off the road, Rossel cruised to the end to claim a second consecutive victory in his Citroën C3 Rally2, moving into the championship lead and finishing 10th overall in the process.
"It's just a shame for Teemu and I'm sorry for what happened to him,” said Rossel. “Honestly, second place would have been a good result for us, but now we have a win.
“I think we have a lot of work to do on the car and myself for Sardinia, but the whole team is motivated and it's a great result for our championship," he added.
Suninen’s demise moved the rest of the field up a position, leaving Kajetan Kajetanowicz to claim the runners-up spot in a Škoda Fabia Rally2. The Pole was in no-man’s land, 1min 12.1sec behind the winner but 4min 42.6sec clear of Chis Ingram’s similar car.
As well as clinching his maiden WRC2 podium, Ingram also took the honours in WRC2 Junior and moved into the championship lead in that category. It wasn’t all plain sailing for the Briton as he overcame punctures in the rough conditions on Friday and Saturday.
Miko Marczyk was fourth in another Fabia. He, too, suffered with tyre damage and trailed Ingram by 1min 14.7sec on only his second-ever WRC rally.
Home hero Armindo Araújo brought his Škoda home 38.5sec behind, followed by Team Hyundai Portugal driver Ricardo Teodósio, who was another 22.5sec in arrears. Jean-Michel Raoux edged fellow Frenchman Frédéric Rosati to win the WRC2 Masters category.
Attrition was high, especially on Friday and Saturday where rough second pass conditions decimated the field.
Some of those to hit trouble included Oliver Solberg, whose i20 N’s steering broke on Saturday, as well Eerik Pietarinen, who stopped with a burst brake pipe on his Volkswagen Polo. Benito Guerra (Škoda) and Georg Linnamäe (Polo) also failed to finish.