David Moyes had a spring in his step in the build-up to the game at the Stadium of Light.
Buoyed by victories over Bournemouth and Hull City, confidence levels hadn’t been affected by defeat at Liverpool, given the spirited nature of the display.
There was still a buzz in training at the Academy of Light, a new-found sense of self-belief among a squad that had started the season in such dismal fashion.
Yet, the 10-game winless streak seems a distant memory given the incredible turnaround.
Moyes was looking forward to seeing what sort of performance his players could produce against the reigning champions, albeit a Leicester City side that are a shadow of their former selves.
And Sunderland did not disappoint, producing their best performance of the season.
Winning the first and second balls, short, sharp passing, creating good openings, Sunderland should have been out of sight in a dominant opening half hour display.
Sunderland were on the front foot from the off, Patrick van Aanholt a constant menace, Victor Anichebe bullying Danny Simpson at full back, chances for Duncan Watmore and Jermain Defoe.
Anichebe should have had a penalty when Wes Morgan pulled him back.
The Foxes had been outfoxed again. Sunderland had pegged them back and were going in for the kill yet they couldn’t find a finish to match their attacking play. But patience paid off.
Just past the hour mark, a Robert Huth own goal opened the scoring for Sunderland, who were denied another penalty shortly after, when Simpson fouling van Aanholt.
It was soon 2-0, Defoe with an instinctive 77th-minute strike after Duncan Watmore’s effort was blocked, his 250th goal in English football.
It was a tension-filled finale, Shinji Okazaki’s 80th-minute finish at the front post for the Foxes meant Sunderland had to dig in late on.
Jordan Pickford helped calm nerves with a superb save to deny Morgan before a wild celebration with the fans behind him. Superb scenes. The Stadium of Light was rocking once again.
Sunderland remain in the relegation zone, but victory over Leicester saw the Black Cats climb to third-bottom, with Moyes’ men now just a point from safety.
It’s a remarkable turnaround. Three wins out of four have also dragged several other teams back into trouble.
Sunderland are only three points off 13th, with arguably now eight teams involved in the relegation scrap, from Crystal Palace down.
The more the merrier from Sunderland’s point of view. There remains a long way to go, of course, but momentum is firmly behind Sunderland.
There are some huge – but winnable games coming up too – with trips to Swansea City and Burnley and a home game with Watford before 2016 is out.
Anything from the games against Chelsea and Manchester United would be a bonus.
Mind, it is never straightforward with Sunderland.
With Lee Cattermole already facing four months out, Sunderland have since lost Paddy McNair long-term, Lynden Gooch for up to three months and now Watmore is braced for a lengthy spell out with a knee injury picked up against Leicester.
The return of Seb Larsson, from knee surgery, and Jan Kirchhoff, from hamstring trouble, to the matchday squad is, therefore, timely.
Larsson didn’t make it off the bench at Anfield, but he came on at half-time against Leicester alongside Kirchhoff – with Steven Pienaar and Jason Denayer substituted with blurred vision and a stomach upset, respectively.
Leicester enjoyed the better of the opening stages of the second half, with Sunderland struggling to regain their rhythm.
It was hardly a surprise given the changes in midfield, but once Larsson and Kirchhoff got to grips with the pace and tempo of the game, Sunderland started to dominate again.
They didn’t do anything flash but kept it simple, kept Sunderland moving and the pair of them combined for the first goal, Huth bundling Kirchhoff’s header into his own net from a Larsson corner.
It was the first goal Sunderland have scored from a set piece – penalties aside – all season. Incredible.
Both played their part in Sunderland securing their third win in four games.
Kirchhoff, in particular, is a big player for the Black Cats provided he can steer clear of the hamstring trouble which has plagued him this season.
With Jack Rodwell also missing with hamstring trouble, Moyes’ options in the centre of midfield are threadbare. Kirchhoff’s return is a huge boost for Sunderland.
His experience, alongside Larsson, will be key to the side maintaining their newly-found momentum which has seen them transform their season.
Sunderland remain deep in relegation strife, but they are showing strong signs they have what it takes to get out of trouble again.
Lamine Kone and Papy Djilobodji were immense at the back, a dominant and powerful display from the duo. Djilobodji made a crucial second-half block to deny Islam Slimani before Sunderland took the lead.
Billy Jones was excellent again at full-back, with van Aanholt linking up well with man-of-the-match contender Anichebe all afternoon down the left. Defoe did what he does best.
Pickford, after an unusually nervous start, kept Sunderland’s lead intact late on.
A real team performance will have pleased Moyes the most.
Denayer and Pienaar, who suffered his blurred vision after a nasty collision with Marc Albrighton before half-time, impressed alongside Didier Ndong in central midfield, Sunderland lining up in a 4-3-3 formation.
Watmore, too, was enjoying his best performance of the season until a Christian Fuchs challenge ended his afternoon, Watmore leaving the pitch on a stretcher.
Leicester are having a tough time of it this season and Sunderland made them look average. Jamie Vardy’s radar was off, Riyad Mahrez lacklustre, with signs of defensive frailties at the back.
Sunderland may be below the Foxes in the table, but they won’t be for long on this evidence.
Moyes has got the Black Cats purring ahead of a huge game against basement side Swansea City this weekend.