At this stage of the season, fine margins can make or break an entire campaign and have mammoth consequences for a club’s future.
With his side 2-1 down, with a wall of sound battering his eardrums, Sam Allardyce made a key tactical switch that would ensure Sunderland went on to win.
Wednesday promises to be a fraught, tension-filled, angst ridden evening on Wearside.Richard Mennear
With 64 minutes on the clock, Allardyce took PFA Fans’ Player of the Month Jan Kirchhoff off and replaced him with the fresh legs of Duncan Watmore.
Fabio Borini was moved inside alongside Jermain Defoe, with Watmore and Wahbi Khazri flying down the wings.
That tactical switch from 4-1-4-1 – playing with effectively three holding midfielders – to a more attack-minded 4-2-3-1 shape reaped instant rewards.
Within three minutes Borini, now in a central position, had levelled from the edge of the area and within six minutes of Allardyce’s tactical tweak, Defoe had scored the winner.
It was a breathtaking fight back with emotion pouring from the stands onto the pitch.
Fine margins, indeed.
With Norwich City beaten by Manchester United and Newcastle United maintaining their horrendous run away from St James’s Park – three points against Chelsea was huge.
It dragged them out of the relegation zone and victory over Everton will mean a tenth straight season of Premier League football – and all the riches that come with it.
Back in October, Allardyce was brought in with a simple remit to keep the club up. He is on the verge of doing just that and his game management against Chelsea was key.
Alongside Vito Mannone’s display and the goals of Khazri, Borini and Defoe, Allardyce’s decision to switch to two up top proved crucial.
With the club’s top flight status on a knife-edge Allardyce had no choice but to go gung-ho.
Impressive Cattermole could have been withdrawn given he had been booked earlier but Allardyce opted to remove Kirchhoff - who wasn’t as dominating as usual - from the action.
Cattermole was then later withdrawn, with replacement Seb Larsson helping calm the midfield down; shouting, rallying, organising in the middle.
The decision to bring Lamine Kone off after just 55 minutes also proved inspired. The £5million January recruit was out of sorts.
The big question now facing Allardyce is whether he changes his starting line-up and system for the first game in seven?
Attack from the off or start with the same set-up knowing they can change it if they struggle to break Everton down? I suspect it will be the latter.
Ahead of Chelsea, Allardyce revealed he uses meditation to cope with the stresses and strains of Premier League management.
With nerves jangling all around him, his coolness and decisive decision making made the difference.
Now, whether that is down to his use of meditation is open to debate. It is more likely a consequence of the years spent honing his craft in dugouts up and down the country.
Either way, it was Sunderland that benefited with the club now in pole position to stay up. But the players now face a different kind of pressure when Everton visit.
Sunderland have produced big results while in the bottom three.
They are out of it again knowing one more win will suffice. Can they manage back-to-back league wins for only the third time this season?
With the character shown against Chelsea, you wouldn’t bet against them.
Wednesday promises to be a fraught, tension-filled, angst ridden evening on Wearside.
Perhaps we could all do with a spot of meditation. It is certainly working for Allardyce.