Genoa needed only a point to confirm their Serie A status and enjoyed a 2-0 home win over Palermo.
Italy international Alberto Gilardino put them ahead after 70 minutes and Giuseppe Sculli doubled Genoa's lead with 20 minutes remaining.
Lecce's result was therefore immaterial, but they ended a disappointing season on a low note when losing 1-0 at Chievo.
Kamil Vacek scored the winner after 78 minutes as Lecce returned to Serie B for the first time since 2008.
The gloom surrounding the club only deepened on 81 minutes when Morris Carrozzieri was dismissed.
In Sunday's other results, Parma beat Bologna 1-0, Roma won 3-2 at Cesena and Fiorentina drew 0-0 with Cagliari.