Captain Javier Zanetti's goal two minutes from time earned Inter the tie. Last weekend, Inter needed a diving header from another Argentine, Hernan Crespo, to salvage a 1-1 draw at Sampdoria.
Inter's only loss in its last 64 games was to Roma last April.
After going 17 years without a Serie A title, Inter is on course for its third in a row and 16th overall. The 2006 title was won after points were stripped from Juventus and AC Milan after being implicated in the Calciopoli match-fixing scandal.
Francesco Totti had given Roma the lead in the first half, but it could not hold on even though Inter played much of the second half with 10 men because it had used all his substitutes when Brazilian left back Maxwell was injured.
"It's a draw that's worth a victory," Inter Milan coach Roberto Mancini said. "Totti scored with their first shot on goal and this changed the game. Then with 10 we suffered."
Shortly before Zanetti's equalizer, Roma's French defender, Philippe Mexes, was sent off for two yellow cards
"It was unjust because the second yellow wasn't a yellow," Roma coach Luciano Spalletti said. "It was absolutely not a foul."