Rejuvenated under Sam Allardyce, the Black Cats were climbing towards Premier League safety amid some encouraging performances.
With the likes of Newcastle United and Norwich City dropping points, a window of opportunity was beginning to present itself.
And the great escape was well and truly on when Chelsea came to town on May 7, 2016.
Goals from Wahbi Khazri, Fabio Borini and a Jermain Defoe stunner saw Sunderland claim a vital win - and they climbed out of the bottom three as a result.
Diego Costa and Nemanja Matic had scored for Guus Hiddink's Chelsea, who saw captain John Terry sent-off late on.
Safety would go on to be secured, but what became of the Sunderland side that beat the Blues on that superb afternoon? We take a look at the varying fortunes of the players who featured that day, and the man in the dugout...
1. VITO MANNONE
Named player of the match by many outlets following his performance in the Chelsea clash, Mannone left Sunderland in 2017 and joined Reading. After loan spells with Minnesota United and Ejsberg he joined Monaco last summer. Photo: Gareth Copley
2. DEANDRE YEDLIN
A key player at the Stadium of Light during his loan spell from Tottenham Hotspur, Yedlin later went on to join local rivals Newcastle United. He remained on Tyneside until January 2021, when he moved to Turkish giants Galatasaray. Photo: LINDSEY PARNABY
3. LAMINE KONE
Kone was one of a trio of new arrivals who kick-started Sunderland's survival bid, but he left the club after their back-to-back relegations. He is now with French top flight side Strasbourg. Photo: LINDSEY PARNABY
4. YOUNES KABOUL
Having formed a fine partnership with Kone, many Sunderland fans were disappointed when Kaboul joined Watford in 2016 - citing 'family reasons' for his desire to move south. The Hornets proved to be the defender's final club, and he now owns a care home in Belgium. Photo: Gareth Copley