Swansea City dented Rafa Benitez's hopes of a record third Europa League trophy with a superb first-leg display.
Benitez is aiming to become the first manager to lift the cup with three different clubs following his success with Chelsea last season and Valencia in 2004.
But his side, currently third in Serie A, will count themselves lucky to be going into next Thursday's second leg at the San Paolo on even terms after being largely outplayed by the Welsh club.
Benitez's Chelsea were dumped out of the League Cup by Swansea at the Liberty Stadium last season, and with rookie manager Garry Monk now in charge they were as impressive as Michael Laudrup's side had been 13 months ago.
Swansea survived a couple of scares in the opening five minutes when Jose Callejon flashed a shot across goal and Marek Hamsik brought a superb save out of Michel Vorm. But Swansea soon went close themselves on a night they dominated, with 10 shots on target to Napoli's one.
Nathan Dyer thought he had given the home side the lead on six minutes but his chip was clawed out of the top corner by Napoli's Brazilian goalkeeper Rafael.
Wilfried Bony then went close with two long-range drives as Monk's side began to grow in confidence against the Serie A giants.
The best opportunity of the half fell to Bony on 23 minutes after Pablo Hernandez put the striker through on goal with a perfect pass, but he took one touch too many and Rafael was able to race out and block his shot.
Napoli looked dangerous on the counter-attack with former Real Madrid forward Gonzalo Higuain leading the line but it was Swansea who were even more threatening. Jose Canas volleyed a shot just over the bar before Ashley Williams wasted a decent opening by heading over five minutes before half-time.
Napoli were much improved for a brief period after the interval but Higuain blazed a volley high and wide after being picked out at the back post by Hamsik.
Swansea regained control of the contest and almost grabbed the lead on 67 minutes when Williams rose to meet Jonathan de Guzman's free-kick with a header but it was palmed away by substitute goalkeeper Pepe Reina, on loan from Liverpool.
Monk pushed for the win in the final 20 minutes sending on Reina's old Anfield teammate Jonjo Shelvey in an advanced midfield role. Shelvey had an immediate impact by finding Wayne Routledge with a precise pass but the winger's shot was turned around the post by Reina.
Man of the match Dyer.
Match rating 7/10.
Referee I Bebek (Cro).
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