Napoli wasted a number of opportunities as they played out a goalless draw with Genk in Wednesday's Champions League clash at Luminus Arena.
The Italian visitors beat reigning European champions Liverpool 2-0 in their Group E opener last month but could not build on that win in Belgium.
Carlo Ancelotti's men hit the frame of the goal three times in the first half and Kalidou Koulibaly also went close as Genk held on for their first point, two weeks on from being thrashed 6-2 by Salzburg.
Arkadiusz Milik in particular was guilty of spurning big chances for a Napoli side who top the group with four points, though Liverpool and Salzburg have a game in hand to play.
Jose Callejon's low shot was parried onto the post by Gaetan Coucke 15 minutes in and Milik had a couple of goes at converting from the rebound, the Poland striker's first shot being blocked and his second clipping the crossbar.
Milik missed another good opportunity 10 minutes later when pulling away from his man but again skimmed the crossbar with his header from inside the six-yard box.
Koulibaly was next to go close for the visitors when his shot was blocked on the line by Patrik Hrosovsky, while Milik headed over when teed up by Koulibaly seconds later as Genk somehow went into the interval all square.
Milik picked off from where he left off early in the second half by heading over once again and, 10 minutes later, Callejon side-footed wide when left all alone inside the box.
Genk, who tested Alex Meret a couple of times across the 90 minutes, managed to keep their opponents relatively quiet in the remainder of the match to claim a point.
What does it mean? Napoli fail to build on Liverpool win
Napoli's victory over Liverpool in last month's opener left them in a strong position, but their away-day struggles in Europe means progression cannot be taken for granted.
They are now without a win in their last seven away group stage matches, last picking up three points in the 2016-17 edition, and this draw against Group E's weakest side could yet prove costly.
Koulibaly a rock at the back
It is now back-to-back clean sheets in Europe for Napoli this season and Koulibaly has played a key part in both shutouts.
The centre-back regained possession more times than any player on the field, had the second-most touches of any player and also offered an attacking threat for good measure.
Milik's misses prove costly
Milik, yet to get off the mark this season, could easily have had a hat-trick inside the opening 45 minutes.
Used as the focal point in attack in the absence of the benched Dries Mertens, the 25-year-old failed to stake his claim and was replaced after 72 minutes.
Genk host Excelsior Mouscron in the Belgian top flight on Sunday, the same day Napoli go to Torino in Serie A.
When the Champions League returns for matchweek three later this month, Genk welcome European champions Liverpool and Napoli make the trip to Salzburg.