Dries Mertens finished off a well-worked team move to give Napoli the 1-0 pre-season victory away to Olympique Marseille.
Piotr Zielinski pulled out of this friendly match after a bout of flu, so summer signing Elmas was given his first start in midfield and made a very good impression at the Stade Velodrome.
Lorenzo Insigne wasted a golden opportunity 10 minutes in, firing straight at the goalkeeper on an Elseid Hysaj cross, while Fabian Ruiz and Radonjic skimmed the woodwork.
Napoli took the lead just before half-time with a well-worked move, as Elmas sent Insigne down the left, his cross was knocked down by Jose Callejon and Mertens finished it first-time from inside the penalty area.
Amin Younes went close to doubling their advantage off the bench, his header palmed away for a corner, then curled another off target.
There was an unseemly incident between Insigne and Dmitri Payet, with the Marseille player appearing to slap the Napoli captain, receiving a yellow card.
No Napoli fans were allowed to buy tickets for the match due to fears over safety.
Marseille 0-1 Napoli
Mertens 38 (N)
Marseille: Mandanda; Sakai (Abdallah 86), Caleta-Car, Kamara, Amavi (Rocchia 76); Sanson, Strootman, Chabrolle (Sertic 60); Sarr, Payet, Radonjic
Napoli: Meret; Hysaj, Manolas (Chiriches 46), Luperto (Maksimovic 46), Ghoulam (Mario Rui 46); Elmas (Younes 46), Fabian (Gaetano 46); Callejon, Mertens (Di Lorenzo 70), Insigne, Milik (Verdi 46)