Sirtautas started his professional career in Atletas Kaunas, in 1989. After a few seasons with the team, he became a team leader, and while playing alongside Saulius Štombergas and Žydrūnas Ilgauskas, managed to lead the team to the LKL Finals twice. During his last season with the team, he averaged 15 points per game. After that successful season, Lithuania national team coaches invited Sirtautas to the training camp for the upcoming EuroBasket, but he did not make it onto the final roster.