Appollonio, a former Cervelo, Team Sky and AG2R La Mondiale rider, tested positive for EPO while riding for Androni-Giocattoli in June 2015.
His ban ended in mid-June 2019, and the Italian Continental team Amore e Vita offered him a contract as he turned 30 just before the end of his ban.
His first race back was slated to be the Sibiu Tour in early July, but paperwork issues meant he had to wait until August and the Volta a Portugal. It didn't take him long to get back into the swing of things. After the race opened with a prologue on Wednesday, he won stage 1, beating Daniel Mestre (W52 Porto) and Matteo Malucelli (Caja Rural) in a bunch sprint in Leiria.
"I'm very happy and it's very strange. Four years was so long," Appollonio said after the stage, according to the Portuguese newspaper Record.
"Today I just wanted to enjoy the race and I was going to see what was going to happen. I suffered most of the day and on the last kilometer I told myself to sprint without thinking about the result.
"It was great to win, especially for family and my friends. It's very strange. I'm not thrilled with the victory because after four years there are more important things in life. Today it was just a bike race."
Appollonio turned pro with the Cervelo test team in 2010 and won a stage of the Tour du Limousin before joining Team Sky in 2011, where he finished second in a stage at the Giro d'Italia and won stages at the Tour of Luxembourg and Tour du Poitou Charentes.
He didn't win any races in his second season with Sky, nor when he moved to AG2R La Mondiale for the 2013 and 2014 campaigns. He dropped from the WorldTour to Pro Continental level in 2015, joining Gianni Savio's Androni-Giocattoli squad, but only lasted half a season before he tested positive for EPO.
The test came in mid-June, a couple of weeks after the end of the Giro d'Italia, and after B-sample analysis confirmed the finding, Appollonio was struck with a ban of four years.