The Italian striker gave Nasr a 42nd-minute lead, against the run of play, but Ismail Al Hammadi's first league goal of the season levelled the scores a minute before the break. Basheer Saeed then put the hosts ahead in the 55th minute, but Mascara silenced the home fans with the equaliser two minutes from time.
Nasr were reduced to 10 men in added time at the end of 90 minutes when Helal Saeed was shown a second yellow card four a foul on Grafite, but Ahli had little time to take advantage of their numerical advantage.
The draw means Nasr (21 points) slip down to third in the Pro League table, one point behind Al Ain, who have a game in hand, and Baniyas, who are level at the top following their 3-1 win away to Al Dhafra. Ahli remain in fourth place on 19 points.
Quique Sanchez Flores, the Ahli manager, is concerned by Ahli's lack of wins at home, but the Spaniard insists he is happy with the style of football his team is producing.
"In general I am very happy with my players," Sanchez Flores said. "We controlled the game, created many chances, but finally gave a present, the foul [which lead to Mascara's second goal], with only two minutes remaining.
"It's would have been worse if we had lost two points and played badly, but we played well, controlled the game against a strong opponent like Al Nasr.
"We lost two points once again at home and we need to work on this, but we have lost just once in 10 games and I am happy with the way my team is playing."
Ahli were the dominant side as the game started off on a soaked pitch following a drizzle. Achille Emana and Grafite kept the Nasr defence busy with numerous forays and could have scored a couple of times in those early minutes, but Nasr's impressive goalgoalkeeper Abdullah Moosa foiled every attempt.
And then the inevitable happened. Just as the fans stood up to sing the national anthem in the 41st minute, to mark the upcoming 41st National Day, Mascara sneaked into the Ahli half and left the home goalkeeper Ali Mesmari stranded with a scorching low shot to the far corner.
Three minutes later, however, the scores were level as Al Hammadi squeezed the ball through a crowded defence. Like most of Ahli's attacks on the night, this one also emanated from the Cameroon international midfielder Emana; a clever back-heel for Tariq Ahmed caught the Nasr defence unaware and the latter chipped the ball across for Al Hammadi to finish off.
Ahli could have doubled their tally five minutes into the second half when Emana played the ball for Grafite, but Moosa did well to keep the Brazilian's effort out. Two minutes later, Luis Jimenez, the Chile international playmaker, went close before Moosa pulled off another good save in the 54th minute, stretching his legs out to deflect Al Hammadi's shot over the bar.
Moosa, however, could do little as Ahli took the lead from the resulting corner as Basheer Saeed's volley took a healthy deflection off Nashat Akram.
Ahli looked like they would hold on to their one-goal advantage until the final whistle, but with two minutes left on the clock, the busy Mascara earned a free kick just outside the box and the Italian blasted it through the tiniest of gaps in the Ahli wall for the equaliser.
"I am very happy with my players and the way we played here," said Walter Zenga, Nasr's Italian coach.
"It is not easy to come to Al Ahli and win a game, but we had our chances.
"Honestly, I believe we are playing well and I hope we can keep this performance going and stay focused."
Follow us @SprtNationalUAE