Leicester piled the misery on David Moyes and pushed Sunderland closer to relegation from the Premier League with a gritty 2-0 win.
Islam Slimani and Jamie Vardy scored to virtually guarantee the champions' own survival and cap a few days to forget for Black Cats boss Moyes.
The Scot's ill-advised comments to a BBC reporter had left him facing a Football Association charge but he is also now staring at relegation with the Wearside club.
Efficient but not effective, the visitors battled hard but the result leaves them bottom - eight points from safety with eight games left.
Leicester have now won six successive games in all competitions under boss Craig Shakespeare and have powered into the top 10 - to sit nine points clear of the bottom three and banish fears of the drop.
Defeat was hard on Sunderland but they came up short after Moyes came into the game under fresh fire following his comment that a BBC reporter might "get a slap" following an interview after their draw with Burnley last month.
Moyes apologised for what he said to Vicki Sparks and the Black Cats issued a statement to say his comments were "wholly inappropriate".
Leicester looked to make him sweat early and Shinji Okazaki fired wide but Sunderland gave as good as they got until Jordan Pickford turned Robert Huth's header over after 15 minutes.
The Black Cats, combative even if they lacked quality, did briefly threaten but Jack Rodwell headed well wide before a scrappy game drifted into midfield limbo.
Despite the champions' winning streak they could not find the space or imagination to break Sunderland down with Vardy touching the ball just nine times in the first half.
Lee Cattermole, back from injury for his first appearance since September, was booked for trying to chop down Demarai Gray as he threatened to break but the fact the Leicester man then overran the ball summed up a uninspiring opening 45 minutes.
Sunderland, though, won the midfield battle with Cattermole, Rodwell and the impressive Didier Ndong upsetting the Foxes every time they tried to find a rhythm.
Gray did at least force England Under-21 team-mate Pickford into a save two minutes before the break, the goalkeeper turning his effort wide, but it was a rare moment of excitement.
Fabio Borini's shot was blocked soon after the restart and Jermain Defoe, who had barely seen the ball, hooked a volley straight at Kasper Schmeichel after 58 minutes.
Leicester's fans vented their frustration at the hosts' inability to break the bottom side down and there was little to suggest there would be any breakthrough until Slimani finally did on 69 minutes.
The striker had only been on the pitch seven minutes but he combined with fellow substitute Marc Albrighton to nod in the winger's cross from six yards.
It was his first club goal of 2017 but Sunderland almost levelled eight minutes later when Victor Anichebe hit the post before Vardy wrapped up victory with 12 minutes left.
Again it was Albrighton who made it with a lung-busting run and, when Sunderland failed to track Vardy, he found the top corner from 15 yards.