Thirty-six-year-old forward Francesco Totti converted Roma's penalty but his side missed out on a win when Erik Lamela contrived to head over from two metres with the goal at his mercy late in the game.
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Lazio, who won the previous three Rome derbies, played the last 20 minutes with 10 men after Giuseppe Biava was sent off for a second bookable offence.
The match was preceded by fan violence and police said two people were stabbed when rival groups of fans clashed in the city. Television pictures showed police in riot gear scuffling with a group of supporters who threw rocks and bottles near the Stadio Olimpico.
Rome mayor Gianni Alemanno said that businesses in the area around the stadium had been forced to close during the clashes.
Fifth-placed Lazio, seven points adrift of a Champions League play-off place, dominated the first half and Hernanes put them ahead with a superb effort in the 16th minute, cutting inside a defender and scoring in the top corner from 25 metres.
Roma, lucky to be just one goal down at halftime, had an ever bigger let off four minutes after half-time when Marquinho handled in the area, only for Hernanes to nonchalantly side-foot wide from the penalty spot.
That proved the turning point and Hernanes compounded his mistake eight minutes later by tripping Miralem Pjanic in the Lazio area.
Totti, who made his Roma debut just over 20 years ago, made no mistake, placing a low shot just inside the left hand post for the ninth Rome derby goal of his career and his 12th goal of the season.
Lazio goalkeeper Federico Marchetti did well to save a Totti free kick at the foot of the post before Argentine midfielder Lamela somehow headed over from almost under the crossbar following a Totti corner.
Lazio's point put them fifth in Serie A with 51 points from 31 games, eight behind third-place AC Milan and a place in the Champions League qualifying rounds. Roma are seventh with 48 points.
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