NOT Cardiff, nor Fulham, nor Norwich.
The biggest threat to Sunderland’s survival after the four-point haul at Manchester City and Chelsea was never going to come from outside sources.
Sunderland have been their own worst enemies this season – own goals, sendings off, set piece shambles.
All have contributed towards the Black Cats’ plight.
If Gus Poyet’s side were going to fall short and fluff their second chance at redemption, it was going to come from beating themselves.
Even in the run-up to yesterday’s pivotal encounter, that was the burning topic of discussion. Would Sunderland allow that dismal run of Stadium of Light custard pies against the Premier League’s lesser lights to continue?
Sunderland answered that question in emphatic fashion.
The benefits of yesterday’s 4-0 victory were immense and on several scores:
1. Getting the monkey off Sunderland’s backs about freezing in these do-or-die encounters at home. With two more Stadium of Light games to come, that was crucial mentally.
2. Moving out of the bottom three gives Sunderland a timely psychological boost ahead of the final week of the season.
3. And from a purely mathematical sense, such a handsome victory – coupled with Norwich’s heavy defeat at Manchester United on Saturday – hands Sunderland an 12-goal advantage in the goal difference column to the Canaries.
But to win this game of games in such fashion was the most convincing demonstration yet that the mentality in Sunderland’s ranks has changed.
There was certainly a different air about the Black Cats at the Etihad and Stamford Bridge. It was perhaps even present in the luckless defeat to Everton prior to that double away day delight.
Something had changed after weeks of malaise following the Capital One Cup final. Rightly or wrongly, that was what Gus Poyet was desperate to remove when he tinkered so dramatically with personnel and formations.
Yet in all three of those performances against the big boys, it would have taken the combined detective skills of Poirot, Tintin and Sherlock Holmes to unearth anyone who genuinely thought Sunderland had a chance.
There was no pressure and Sunderland revelled in that freedom.
Yesterday was different. It was a test of mettle, a test of character and almost a test of manhood.
Sunderland rose to the challenge and performed.
To pick out one player – which would perhaps be unjust given such a harmonious display – Jack Colback has epitomised this new-found doggedness around Poyet’s ranks.
Colback’s future is uncertain. There have been rumours circling about him joining Newcastle (albeit senior Magpies sources have played down that interest) and yet he was again excellent yesterday – driving forwards and bridging the gap between Connor Wickham and the midfield.
The same applies to Seb Larsson, with the Swedish international similarly in the final few weeks of his contract and seemingly on his way out of the club.
Far from panicking at failing to get their noses in front in the opening 10 minutes, there was a calmness around Sunderland, even after Cardiff had begun to take the sting out of things.
Yes, Sunderland were guilty of moving the ball too slowly, yet they did not resort to kick and rush.
Sunderland kept their composure, continued to pass the ball and defended without fuss, with the two centre-halves again excellent and Lee Cattermole breaking up Cardiff’s half-hearted attacks, despite Jordon Mutch’s attempt to wind the midfielder up.
That patience paid off as man-of-the-moment Connor Wickham pounced on Cardiff’s pathetic defending to loop home the opener.
It was the perfect platform.
Sunderland were able to control proceedings – keeping possession, finding space and never allowing Cardiff a sniff.
Once another piece of catastrophic defending from Cardiff had given Sunderland the second, the buoyancy around the Stadium of Light was a reflection of how pivotal that killer goal on the stroke of half-time was.
Enormous credit must go to Phil Dowd for having the fortitude to make such a huge call, but he undoubtedly made the right one.
Juan Cala’s shirt-pull on Wickham began outside the box and continued into the area – meeting the criteria for a penalty – and he attempted to play the advantage without any arriving.
Perhaps the media attention which surrounded West Ham winger Matt Jarvis – fouled inside the area against Arsenal a fortnight ago while staying on his feet – played on Dowd’s mind.
But it still needed Dowd to make a split-second judgement. In an age of constant referee-baiting, the official deserves every pat on the back he receives.
It was the game-changing moment. Cardiff delivered a couple of scares from set pieces, yet never really threatened to pull off a comeback with 10 men.
Despite Ole Gunnar Solskjaer introducing every offensive option on his bench, the brutal truth was that Cardiff were poor. Very poor.
That shouldn’t detract from the quality of Sunderland’s performance though.
Netting a third and fourth added gloss to the scoreline and ensured Sunderland’s players could revel in the finale; enjoying the buoyancy of the crowd from such a convincing win.
Plenty of ghosts will have been banished in those seemingly meaningless last few minutes.
That was important.
Sunderland need the Stadium of Light to offer comfortable surroundings in those crucial last two games, rather than worrying anymore about playing at home.
Those visits of West Brom and Swansea still provide Sunderland’s trump card in the battle to avoid the drop.
Two wins over the final three games will essentially confirm Sunderland’s Premier League status now, given their superior goal difference over each of the bottom three.
Realistically, four points may well be sufficient, unless Fulham and Norwich can win both of their last two fixtures.
The test for Poyet’s men now is to avoid letting complacency set in.
Yes, they have produced a remarkable turnaround to take seven points from three games, yet it still requires a big effort to get over that finishing line.
But the manner in which Sunderland have performed in these last few weeks indicates players who have grasped how perilous the situation was and duly reacted, rather than throwing in the towel.
These lot really don’t want a relegation on their CVs.