Lionel Messi scored a superb Champions League hat-trick as Barcelona ran Ajax ragged in their Group H opener at the Nou Camp.
The Argentinian striker was at his effortless best, despatching a fine first-half free-kick and then producing two clinical finishes either side of Gerard Pique's header.
Ajax were passengers in the second period and were denied even a consolation when Victor Valdes saved Kolbeinn Sigthorsson's penalty.
Prized signing Gonzalo Higuain put Napoli ahead 29 minutes in on a rainy night at San Paolo Stadium by heading home a cross from Camilo Zuniga, after which Dortmund coach Juergen Klopp was sent off for protesting.
Higuain was also at the centre of the action when goalkeeper Roman Weidenfeller was shown a red card for using his hands outside his area to deny the striker in first-half added time.
Lorenzo Insigne doubled Napoli's lead in the 67th minute with a free-kick which curled into the top corner.
Zuniga scored an own goal to give Dortmund hope in the 87th minute, but Napoli held on.