Sunderlad won three vital points in their push for promotion thanks to a first half goal from Aiden McGeady.
With Portsmouth slipping up earlier in the day and the Black Cats recording the third-highest attendance in the UK, it was an excellent day for Jack Ross and his side.
The result itself was anything but straightforward, however.
Bradford City applied a lot of second half pressure and the hosts looked to have been handed an incredible slice of luck when Jon McLaughlin seemingly turned a Jack Payne shot over the line.
It was one of a number of decisions that Bradford felt went against them in a tense encounter.
Sunderland were greeted by an almighty roar as they walked out in front of an incredible attendance, but the game itself quickly settled into a sedate rhythm.
Bradford City have been on a good run in recent weeks and lining up in a midfield diamond, kept their shape and looked to jeep the game as narrow as possible.
The Black Cats were patient in their build-up play but it was the visitors with the first sight of goal, David Ball curling a free-kick over the bar from the edge of the area.
Jack Ross's side responded well and created a few promising openings of their own.
Josh Maja and Lynden Gooch twice combined well on the edge of the area, Maja shooting across goal before Gooch fired wide on his weaker left foot.
After missing the Portsmouth defeat due to illness, Maja looked lively and almost scored an ingenious opener.
Bryan Oviedo powered down the left and sent in a low cross, Maja turning it just wide of the far post with a deft flick.
Sunderland were the better side, but Bradford were a threat then they won the ball back, committing their central midfielders quickly to the counter.
They should have been ahead when Sunderland switched off from a throw-in. Jack Payne picked up the ball and danced his into the box, beating a number of players before dragging wide.
That warning sign was heeded and Sunderland were soon ahead, albeit thanks largely to Richard O'Donnell in the Bradford goal.
He couldn't gather a Maja shot and under pressure from Chris Maguire, spilled the ball into a dangerous area. Aiden McGeady scored with a composed finish, comfortably beating O'Donnell low to his left.
That settled the nerves in the Stadium of Light and there was almost a second just before the break, O'Donnell almost failing to prevent a McGeady drive from 20 yards.
The hosts started the second half well but Bradford were adamant that they should have had a penalty when Max Power arrived in the box to challenge Ball.
Moments before, Jon McLaughlin had been indebted to Luke O'Nien for an excellent covering clearance after the goalkeeper rushed off his line.
O'Nien was again impressing in the unfamiliar right-back position.
Sunderland steadied and came close to doubling their lead from successive set pieces.
A wicked cross from Bryan Oviedo was just header over by Hope Akpan, with Tom Flanagan then rising at the near post to nod a free header wide.
The centre-back was involved in a significant flashpoint 15 minutes from the end. He had dribbled into a dangerous area from deep but after being robbed of the ball, Nathaniel Knight-Percival appeared to prevent him from getting back to his feet and tracking back. There looked to be a scuffle as play carried on and the visitors were incensed that Flanagan only saw yellow.
Their mood worsened even further soon after. Payne struck one from range but there seemed to be little danger to McLaughlin, who spilled the ball and had to edge back towards goal to try and prevent it trickling over the line. The ball looked to have gone in but the referee played on, with David Hopkin booked for his demonstrations on the touchline.
Sunderland were under pressure but substitute Duncan Watmore almost settled the contest with a clever header, O'Donnell doing well to turn it over the bar.
The lively forward then won one of the biggest roars of the afternoon as he carried the ball from near his own box right up to the byline, drawing a foul and precious time for his team.
Sunderland held on for three crucial points.
Sunderland XI: McLaughlin; O'Nien, Flanagan, Baldwin, Oviedo; Power, Cattermole; Gooch (Wyke, 83), McGeady, Maguire (McGeouch, 88); Maja (Watmore, 75)
Subs: Ruiter, Ozturk, James, Sinclair
Bradford City XI: O'Donnell; Caddis, McGowan, Knight-Percival, Chicksen (O'Connor, 88); Akpan (Brunker, 85), O'Brien, Payne, Ball; Doyle (O'Brien, 80), Miller
Subs: Wilson, Wood, Devine ,Goldthorp
Bookings: Gooch, 60 Chicksen, 62 Payne, 67 Flanagan, 74 Caddis, 90 Oviedo, 90 O'Brien, 90