After threatening a repeat of last season's collapse, which saw them miss out on a Champions League place, Leicester are nearly over the line.
With the FA Cup final against Chelsea on Saturday, Brendan Rodgers and his players could have been forgiven for conserving themselves for Wembley at the expense of this game.
But after being beaten by United on the final day last season, winning just three of their last 14 games, securing a top-four spot is arguably as important as securing a first FA Cup triumph.
After drawing with Southampton and suffering a shock home defeat to Newcastle, the wheels looked like they were coming off again, with Leicester flagging with the finish line in sight.
But, aided by United boss Ole Gunnar Solskjaer, who responded to having to play three games in five days by making wholesale changes, Leicester proved their mettle with a deserved win.
They now have an eight-point advantage over fifth-placed West Ham and, barring a bizarre sequence of results, should be gracing the Champions League next season.
Having beaten Aston Villa on Sunday, and with arch rivals Liverpool returning to Old Trafford on Thursday for their rearranged game, Solskjaer made 10 changes to his starting line-up.
Only Mason Greenwood kept his place, while there was a debut for 19-year-old United winger Anthony Elanga and a first Premier League appearance for Amad Diallo.
The visitors took the lead in the 10th minute, Youri Tielemans sending a looping ball into the United area, intended for Jamie Vardy.
Vardy unselfishly left it, allowing Luke Thomas to apply an emphatic volleyed finish to send the ball fizzing past David De Gea and into the top far corner.
The lead lasted just five minutes, United drawing level through in-form Greenwood, who plundered his eighth goal in 11 games.
Amad showed great desire to win the ball from Thomas down the right, then slotted the ball inside to Greenwood, who looked to have few options.
But the young forward's quick brain and quick feet enabled him to shift the ball onto his right foot and create enough space to send a low shot across Kasper Schmeichel into the far corner.
With a torrential downpour making the playing surface slippery, passes frequently went awry, with little in the way of quality after the breathless opening to the game with the first two goals.
De Gea made a fine save at point-blank range from Kelechi Iheanacho just before the hour, as the game opened up.
An injection of quality was required, with both managers making changes midway through the second-half, Solskjaer bringing on Edinson Cavani and Marcus Rashford, while Rodgers introduced James Maddison.
The Foxes took the lead in the 66th minute from an Albrighton corner, Caglar Soyuncu rising above Nemanja Matic to beat De Gea with an unstoppable header for his first goal in 18 months.
Tielemans came close to making it 3-1 to Leicester, but was unable to turn in Vardy's header at the far post, colliding with it in the process.
Soyuncu's goal confirmed Manchester City as champions for the third time in four years, but Leicester had just as much to celebrate at the final whistle, having all but consigned last season's collapse to the past with this fine win.
