Paris Saint-Germain were staring down the barrel of a group-stage exit after Dries Mertens' 77th minute goal looked to seal three points for Napoli.
But the Argentinian curled in a sensational left-footed strike past David Ospina in the 93rd minute to rescue a point.
Lorenzo Insigne struck first in the 29th minute for the Italians, only for Thomas Tuchel's side to draw level through a Mario Rui own goal in the 61st minute.
Mertens poked home from close range but Di Maria produced the magic when it mattered most.
Despite his team-mate's late heroics, Neymar was fuming at full-time.
He did not shake hands with anyone, marched straight off and kicked a plastic object.
PSG had won their first ten league games while averaging nearly four goals per game to sit top of Ligue 1.
But they cannot replicate that form in Europe, losing 3-2 to Liverpool in the first round of group fixtures.
Liverpool hammered Red Star Belgrade 4-0 in the night's other match to lead Group C on six pouns.
Napoli are second on five points and PSG third with four.
After failing to get past the Round of 16 in the past two seasons, another early elimination could be looming unless PSG improves.
For Napoli coach Carlo Ancelotti, meanwhile, it was an enjoyable moment against his former club.
Source: Read Full Article