Sunderland, managed by former United stalwart Steve Bruce, were heading for their first win at Old Trafford since 1968 when defender Ferdinand deflected a left-foot drive from Patrice Evra into the net three minutes into added time.
Earlier, Darren Bent gave the visitors a seventh-minute lead with a crisp turn and low right-foot shot from the edge of the penalty area past goalkeeper Ben Foster.
"We are really disappointed," Bent told ESPN. "I think the boys played really well and we worked really hard.
"You know what Man United are going to do at home, they are going to come at us, come at us, come at us ... but obviously we are dejected not to get all three points."
Elsewhere, Hassan Yebda's header handed Portsmouth their first points of the season in a 1-0 win at promoted Wolverhampton Wanderers.
"We've waited a long time for it," manager Paul Hart told Sky Sports.
Portsmouth's dismal form had seen the struggling south coast club become the first English top flight side to lose their opening seven league games of the season for 79 years.
"It's one win and we have got to build on that and start climbing the table," Hart said. "We played some great stuff in the first half and defended absolutely brilliantly in the second."
Niko Kranjcar's first Spurs goal and a header by fellow Croatia international Vedran Corluka cancelled out a third-minute strike from Ricardo Gardner and a Kevin Davies header.
Ninth-placed Burnley made it four home wins out of four by beating Birmingham City 2-1 while Hull City put last week's 6-1 thrashing by Liverpool behind them with a 2-1 home victory over Wigan Athletic.
