The hosts were denied victory by Domenico Berardi, who levelled late in the Stadio Olimpico clash after an own goal had given the Serie A table-toppers the lead
The Giallorossi went ahead midway through the first half when Alessandro Longhi put the ball in the back of his own net and a slim victory looked likely as the game wore on.
But a goal from Domenico Berardi in the dying seconds silenced the Stadio Olimpico and consigned the capital club to another draw following their 10-match win run which they began the season with.
The likes of Mehdi Benatia, Francesco Totti and Mattia Destro were unavailable to Rudi Garcia's men in the clash with the newly promoted side, who had achieved impressive draws with Lazio and Napoli earlier in the campaign.
Miralem Pjanic air-kicked his attempt at giving the Giallorossi the lead early on, while Roma shot-stopper Morgan De Sanctis had to be on his toes to keep Berardi's long-distance shot from rustling the back of the net.
It took 19 minutes for the hosts to boost into the lead. Adem Ljajic put Alessandro Florenzi through on goal and, though Gianluca Pegolo pulled off a super save to deny the attacker, Longhi subsequently put his own team one goal down when he tried to clear the ball.
Pegolo again proved himself in impressive form when he leapt to keep Ljajic's goal-bound effort from rocketing in with a low save, keeping Eusebio De Francesco's charges just 1-0 down at the halfway mark.
The second half was a much livelier affair than the opening 45 minutes. Ljajic's duel with Pegolo continued, and the latter got a hand to a pass from the former at the byline to deny what would have been a sure-fire second Roma goal.
The visitors looked for ways to contain Roma attacks and break down the hosts' defence, however, Sassuolo were consistently thwarted in their attempts and rarely tested the Stadio Olimpico residents.
That was until the final few minutes, when De Sanctis was forced into a save with his foot to keep out Antonio Floro Flores.
But the underdogs fought until the very death and were rewarded in the fourth minute of stoppage time when a goalmouth scramble allowed Berardi to blast under the crossbar for a dramatic equaliser.