Napoli fumbled a 2-0 lead to draw 2-2 with Wolfsburg, but reached the Europa League semi-final 6-3 on aggregate.
They go into the semi-final draw with Fiorentina, Dnipro and Sevilla.
The Partenopei were feeling confident after a huge 4-1 victory in Germany, but Rafa Benitez took no chances and fielded a strong line-up, missing Christian Maggio, Kalidou Koulibaly, Juan Camilo Zuniga and Michu through injury. Wolfsburg were without stars Andre Schurrle, Kevin de Bruyne, Aaron Hunt and Vieirinha, but threw in Nicklas Bendtner for Bas Dost.
Ivan Perisic forced Mariano Andujar into a very tricky save in the opening minute, as the bounce was taking it over him into the far top corner.
Bendtner’s glancing header whistled wide, as did a Perisic effort and a Christian Trasch volley, as the hosts sat back early on.
It was all Wolfsburg and Bendtner rose above the crowd to nod inches past the far post, while Andujar smothered the Maximilian Arnold long-range attempt.
Andujar was the only goalkeeper making any saves and parried from Bendtner again at the near post. Napoli had their first and only chance of the first half with Gonzalo Higuain’s volley on the turn going off target.
The pressure was irrelevant, as the Partenopei took the lead straight after the restart. Higuain’s smart cross-field pass sent Callejon clear on the counter and his shot took a deflection off Ricardo Rodriguez to loop over Diego Benaglio’s fingertips.
That goal seemed to lift the tension off Napoli, as Higuain then dribbled past two players to turn his angled drive just wide.
Lorenzo Insigne came off the bench and put in a series of wonderful crosses, including the one for their second goal. Higuain laid it off for Mertens, whose shot was parried by Benaglio, but ricocheted back off the Belgian into the net.
Wolfsburg did get a consolation goal, as they had in the first leg, with Klose nodding in an Arnold cross.
Moments later there was a second, Guilavogui’s cross from the right met by a brave Perisic header into the far top corner. He got a knock to the head too from Giandomenico Mesto’s high foot.
However, it was too little too late for Wolfsburg.
Napoli 2-2 Wolfsburg (6-3 agg)
Scorers: Callejon 50 (N), Mertens 65 (N), Klose 71 (W), Perisic 73 (W)
Napoli: Andujar; Mesto, Albiol, Britos, Ghoulam; David Lopez, Inler; Callejon, Hamsik (Insigne 60), Mertens (Henrique 83); Higuain (Duvan Zapata 68)
Wolfsburg: Benaglio; Trasch (Dost 79), Naldo, Klose, Rodriguez; Guilavogui (Jung 75), Luiz Gustavo; Perisic, Arnold, Caligiuri; Bendtner
Ref: Cakir (TUR)