 Tziolis initially established himself as a first-team player for Panathinaikos ahead of Igor Biscan during the 2006–07 season.In April 2007, he scored a goal helping his club break Skoda Xanthi's unbeaten home run in the Superleague Greece and secure a place in the Greek Cup final against Larissa.By the end of 2007–08 season Tziolis was close to his exit from Panathinaikos but new manager Henk Ten Cate chose to keep him.