Mertens akahwina imwe menduru yevakundi musi wa22 Zvita 2014 mushure mekukunda kweNapoli paJuventus muSupercoppa. Kunyangwe achinyanya kushandiswa sechinotsiva, akaenderera mberi nehunhu hwake hwakanaka hweNapoli mumwaka unotevera nehafu, achiwana zvibodzwa gumi uye achipa rubatsiro gumi nerimwe mumakwikwi ese muna 2014-15, uye zvimwe zvibodzwa gumi nerimwe muna 2015-16.
. Nhamba yake mumushandirapamwe wekupedzisira yaisanganisira brace muNapoli yakabatana-yakakura kukunda kumucheto muEuropa League, kukunda 5 <unk> 0 pamusoro peBelgian side Club Brugge. Mertens akawanawo hat-trick muhafu yechipiri mukukunda 6-0 kukunda Bologna musi wa 19 Kubvumbi 2016.