A game delayed half an hour by United’s late arrival due to traffic congestion burst to life in the 70th minute with three rapid-fire goals that allowed Spurs to trim Leicester’s advantage back to seven points.
Leicester, 2-0 winners at Sunderland earlier in the day, remain overwhelming favourites for the title, but Spurs’ display showed that Mauricio Pochettino’s side will not give up without a fight.
Pochettino had not beaten United in six previous attempts, first with Southampton and then Tottenham, and Spurs had not scored against them in three games under him. Both trends were reversed in stunning fashion.
The result, Spurs’ first home league win over United in 15 years, had the additional effect of securing Leicester’s place in the Champions League and United’s hopes of joining the Foxes at Europe’s top table are fading.
Spurs’ first chance, a close-range effort from Harry Kane that David de Gea blocked, would not have stood anyway due to offside, but the momentary excitement seemed to enliven both crowd and team.
Christian Eriksen curled narrowly wide from wide on the left and then made a gilt-edged chance for Lamela with a flighted left-foot cross, only for the stooping Argentine to head wide from six yards.
Moments later Kyle Walker turned Marcos Rojo inside-out on the Spurs right, but 18-year-old Fosu-Mensah, preferred to Matteo Darmian, slid across brilliantly to block the England right-back’s cross.
Van Gaal made a change at half-time, sending on Ashley Young for Marcus Rashford, but rather than move Anthony Martial up front, he tasked Young, who habitually plays on the wing or at full-back, to lead the line.
Young spent most of the second half as a spectator as Spurs began to impose themselves, with De Gea repelling a succession of potshots from Eriksen, Eric Dier and Kane.
But despite remaining out on the left, Martial began to exert an influence, teeing up Jesse Lingard to shoot wide and then cutting in from the left, leaving three opponents in his slipstream, and stinging Hugo Lloris’s palms with a crisp drive.
Back came Spurs, De Gea kicking Danny Rose’s deflected cross away and Kane seeing a cross headed clear by Fosu-Mensah, who hobbled off moments later to be replaced by Darmian.
Within seconds Darmian found himself ambling over to close down Eriksen, but the Dane cleverly took him out of the game with a deft left-foot cross and Alli steamed in at the back post to apply the finish.
Four minutes later Lamela’s free-kick from the left was met by centre-back Alderweireld, whose header found the bottom corner, and two minutes after that Rose crossed for Lamela to sweep in the third.
It took a finger-tip De Gea save to prevent Kane making it 4-0 with a header and Walker then hit the post after sliding in to meet Lamela’s drilled cross-shot from the left.
Divock Origi came off the bench to score twice as Liverpool beat Stoke City 4-1 at Anfield on Sunday for their biggest home win this season.
Victory saw the Reds leapfrog the Potters into eighth place in the Premier League table.
Origi had been on the pitch less than five minutes after replacing Sheyi Ojo at half-time when he scored his second goal in as many games, nodding home James Milner’s cross in front of the Kop.
The Belgian got a fortuitous second goal, his cross going directly into the net as Jurgen Klopp’s side recorded only their second league win on home turf in 2016, good preparation for the second leg of their Europa League tie against Borussia Dortmund on Thursday.
