A brief flicker of something better, an all too predictable let down.
Sunderland had improved from their tame showing at Vicarage Road, starting with intent and fight here.
They did not create a clear cut chance in the opening hour but their delivery was much improved, Lee Cattermole's return bringing a significantly greater presence in the middle of the park.
For 60 minutes, they were level in all aspects of the game, perhaps even the better side.
Then they flagged, faded, as we have seen far too often.
They waited too long to change, dropping deeper, losing their composure.
Craig Shakespeare seized the moment and within 20 minutes it was all over.
Substitute Marc Albrighton crossed for Islam Slimani, also brought on from the bench, his towering header unstoppable even for the again excellent Jordan Pickford.
Albrighton then raced clear and passed for Jamie Vardy, who with one sweeping drive surely drew the curtain on Sunderland's Premier League tenure.
Six games now without a goal.
Eight games left, and little hope.
A brief flicker of improvement giving way to familiar deficiencies.
Deficiencies that will send the Black Cats into the Championship.
The importance of Cattermole's return was obvious from the off.
Matching Leicester's now traditional and trademarked 4-4-2, Sunderland were able to match them with Rodwell and Cattermole showing tenacity and some composure in the middle of the park.
That said Leicester's quality in the wide areas could not have been clearer.
A sharp cross to the front post was turned just wide by Shinji Okazaki, with Riyad Mahrez twisting and turning on the opposite flank and causing Bryan Oviedo real problems.
Jordan Pickford made his first notable save of the game as Robert Huth's looping header from a Mahrez threatened to drop in at the far post, but Sunderland were also threatening, Didier Ndong firing in a superb cross from the right and Rodwell heading over from a corner.
Seb Larsson's set-piece delivery was much improved and better quality out wide meant he was getting plenty of opportunities to deliver them.
His weakest corner gave Leicester a chance to break, Cattermole forced to take a yellow card by cynically challenging Gray who was racing clear.
Little goal mouth action preceded the half-time whistle, though Jordan Pickford had to be at his very best to turn a Gray cross wide of the far post with a breathtaking leap.
The importance of that save quickly became clear as the Black Cats came out for the second half on top and playing with confidence. Fabio Borini broke but his shot was blocked after perhaps taking one touch too many, while Seb Larsson forced a save from Schmeichel, albeit a routine one.
Larsson then blazed a free-kick over the bar from 20 yards but the raising din in the away end reflected a growing confidence. His delivery from the right minutes later was much better, cleared to the edge of the box where Defoe took one touch before volleying at Schmeichel.
It was not until the 62nd minute that the Foxes registered their first real effort of the half, Robert Huth somehow beating four Sunderland players to a Christian Fuchs header, Pickford getting down to save with relative ease.
By now Leicester had introduced Islam Slimani and Marc Albrighton, for the first time beginning to exert real control on the game. Lamine Kone had to be alert to clear a wicked cross as Slimani circled, Sunderland sending Victor Anichebe to warm up.
Struggling to keep the ball and move up the field, the Nigerian's qualities were a clear necessity.
Before he could emerge, the crucial goal had been scored.
Albrighton cut on to his right foot and delivered a superb dipping cross to the penalty spot, and this time Slimani got there first, Pickford powerless to stop it down to his right.
Khazri and Anichebe were introduced but by then the damage was clearly done, Vardy racing onto a through ball and forcing another save from Sunderland's goalkeeper.
Anichebe was unlucky to see his left-footed effort deflected onto the post, Defoe firing into the side netting on his weaker foot on the follow-up.
That proved to be nothing but a brief hint of a revival, Sunderland down and surely out moments later.
Albrighton advanced down the left, before laying the ball off for Vardy. The striker took just one touch before firing into the top corner, a fine goal that surely drew the curtain on Sunderland's time in the Premier League.