Having already lost to both AC and Inter Milan this season, Roma were again found wanting against one of their main title rivals, and were undone by a Napoli counter nine minutes before the break.
“We were badly unbalanced in that situation,” Roma manager Gian Piero Gasperini told DAZN.
“It was our error, the only time we really allowed that counter-attack, even in the second half when we were chasing the game.”
Two successive wins had taken Roma clear at the summit, but in a congested top six, Milan moved to 28 points and claimed top spot by defeating Lazio 1-0 on Saturday, and Napoli are behind the leaders on goal difference.
Roma are one point behind in fourth, level with third-placed Inter Milan. Bologna, who host Cremonese on Monday, are three points further adrift in fifth, alongside Como.
There was a frantic end-to-end start with Napoli causing more danger early on in front of goal.
A quick attack from the visitors brought Roma keeper Mile Svilar out of his area to deny Noa Lang before he scrambled back to stop Rasmus Hojlund’s follow-up effort and Giovanni Di Lorenzo volleyed an effort into the side netting.
Lang then twisted and turned his way into the area, and his cross-shot almost caught out Svilar but the Roma keeper got one hand across to bat the ball away.
Roma threaten
Roma finally began to threaten. Lorenzo Pellegrini’s pullback from the byline almost set Evan Ferguson up for a tap-in but Amir Rrahmani got there first to clear for a corner.
Ferguson headed over another chance, and just when it appeared Roma were getting the upper hand, Napoli broke quickly to take the lead.
Hojlund sent Neres running through one-on-one with Svilar and he coolly chipped the ball over the onrushing keeper to net his third goal in two Serie A games.
“I asked the guys to look the opponent straight in the eye from the start and they did,” Napoli boss Antonio Conte told DAZN.
Napoli controlled the tempo after the break, never committing too many men forward and Roma struggled to make any inroads towards an equaliser, while the visitors were always a threat on the counter.
Roma sent on Paulo Dybala and Neil El Aynaoui just after the hour mark, having already replaced Ferguson with Tommaso Baldanzi at the break but the hosts never troubled the Napoli keeper until the 90th minute.
Baldanzi forced Vanja Milinkovic-Savic into a late save, but it was too little and too late from Roma and Napoli earned back-to-back wins in a title race with little margin for error.
“The boys are showing that they have enthusiasm, desire and determination,” Conte added.
“We must not lose this because last year it led us to the Scudetto,” he added.