Sporting won 17 out of 17 home matches on their way to a championship triumph last season and the Lions began the new campaign with another convincing win at Alvalade against a largely inoffensive Rio Ave.
A first-half brace by man-of-the-match Pedro Gonçalves was reward from a dominant opening 45 minutes from Sporting.
Viktor Gyökeres made it 3-0 just after the hour mark, before Clayton scored a fine consolation goal for the visitors in the 90th minute.
Tom Kundert reports from Alvalade.