Messi fires Barca to emphatic win
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 for large parts of the 4-0 defeat and were denied even a consolation when Victor Valdes saved Kolbeinn Sigthorsson's penalty.
Schalke had a much easier time of it at home to Steaua Bucharest, claiming a 3-0 win.
Atsuto Uchida opened the scoring after 67 minutes, with Kevin Prince-Boateng (78) and Julian Drexler (85) adding the gloss.
Napoli were 2-1 winners at home over last year's beaten finalists Borussia Dortmund in Group F.
It could have been worse for Jurgen Klopp's side, who lost goalkeeper Roman Weidenfeller to a red card just before the interval following goal-preventing handball outside the area.
Napoli were already ahead through Gonzalo Higuain's 29th minute effort and doubled their advantage through Lorenzo Insigne in the 67th minute.
Dortmund got one back in the closing moments when Camilo Zuniga put the ball past his own keeper.
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