Lorenzo Insigne's early penalty looked to have put third-placed Napoli on track to move within two points of league leaders AC Milan with five matches remaining, but El Shaarawy's late intervention left them four points behind. Reigning champions Inter Milan are two points behind their city rivals in second place, but with a game in hand.
Luciano Spalletti's Napoli are hoping to lift a first Scudetto since the second Diego Maradona-inspired triumph in 1990, but this bad-tempered draw could prove decisive come the end of the campaign.
The point was not much help to the top-four hopes of Jose Mourinho's Roma, who missed the chance to cut the gap to fourth-placed Juventus to three points.
It has been a potentially ruinous spell for Napoli, following a 3-2 home loss to Fiorentina last time out.