Darren Bent's penalty looked to have condemned High Court-bound Portsmouth to their 18th league defeat of the season before Dindane's header five minutes into stoppage time.
Portsmouth manager Grant was dismissed along with home defender Ricardo Rocha and Sunderland pair Lee Cattermole and David Meyler after storming onto the pitch at half-time to vent his fury at hapless referee Kevin Friend.
Sunderland - without a win since beating Arsenal on October 21 - took the lead in controversial circumstances after only 12 minutes.
Bent raced in behind the Portsmouth defence to latch onto Kenwyne Jones' neat flick before appearing to be tripped by defender Rocha.
Referee Friend pointed immediately to the spot even though replays showed Rocha made no contact with Bent.
To add to Portsmouth's sense of injustice, Friend brandished a straight red card, initially to midfielder Hassan Yebda before correcting his mistake and sending off the bemused Rocha.
Friend's error seemed to spur on ten-man Pompey and the hosts were unlucky not to find themselves on level terms in the 22nd minute.
Frederic Piquionne headed Jamie O'Hara's centre into the path of Dindane and the Ivory Coast star turned beautifully on the penalty spot only to see his low right-foot drive diverted wide by Craig Gordon's outstretched left leg.
Grant was forced to watch the second half from the television gantry after being sent to the stands for furiously remonstrating with the hapless Friend as the teams went off for the interval.
Sunderland were also reduced to ten men within eight minutes of the re-start after Cattermole was booked twice in the space of five minutes.
Cattermole head already been shown a needless yellow card for over protesting at the award of a free-kick when he went in late on Dindane.
Bent should have put the game beyond Pompey's reach in the 65th minute, finding himself one-on-one with David James only to be denied by a brilliant flying save from the England goalkeeper.
The Black Cats were denied by the woodwork from the resulting corner as Matt Kilgallon's powerful half-volley came crashing back off James' right-hand post.
Substitute Meyler set up a nervy final four minutes for his side after joining the list of dismissals following a vicious elbow attack on Steve Finnan only a minute after coming on.
Meyler was made to pay when Dindane ghosted in at the back post to nod in O'Hara's cross.