Marcus Rashford scored twice on his Premier League debut to help Manchester United to a 3-2 win over Arsenal at Old Trafford.
The 18-year-old striker, who had hit a double just three days ago against Midtjylland in the Europa League, struck twice more inside four first-half minutes before Danny Welbeck pulled a goal back before the break against his old club.
Ander Herrera's deflected strike - set up by Rashford - restored the hosts' two-goal lead in the 65th minute, only for Mesut Ozil to peg them back again four minutes later.
Arsenal pressed for an equaliser in the closing stages but were unable to find one as their title challenge faltered to leave them five points behind leaders Leicester and three off local rivals Tottenham.
The visitors started the game the quicker and should have taken the lead after seven minutes, Nacho Monreal hitting his shot too close to David de Gea when one-on-one after Ozil had flicked a fine first-time pass over the top of the United backline.
Rashford showed a flash of what he is capable of soon after, cutting in from the left and bursting between Hector Bellerin and Gabriel before being brought down on the corner of the box. Memphis Depay forced Petr Cech into a save from the resulting free-kick.
The game burst into life just before the half-hour though as Herrera dispossessed Theo Walcott inside the Arsenal half before playing the ball wide to Guillermo Varela. Gabriel stretched to cut out the full-back's cross but could only divert it into the path of Rashford (29) who fired high past Cech.
Just three minutes later and Rashford was at it again, Jesse Lingard lofting in a cross from the right and the 18-year-old finding space in the box before nodding into the far corner.
The Gunners were briefly rattled but soon regained their composure and pulled a goal back five minutes before half-time as Welbeck headed in from Ozil's free-kick.
The second half started with the visitors on the front foot and United happy to sit back and invite the pressure.
However, Arsene Wenger's side failed to really open up the hosts' defence and found themselves 3-1 down as the game approached the three-quarter mark.
Juan Mata released Rashford down the right channel and the academy graduate held up the ball well before feeding Herrera, whose first-time shot took a huge deflection before finding the net (65).
Ozil cut the deficit again four minutes later as he fired in the rebound after De Gea had brilliantly saved Welbeck close-range effort. The German didn't strike his shot cleanly but it bounced high into the net to give the goalkeeper no chance.
Arsenal went in search of an equaliser in the final 20 minutes but were frustrated by the makeshift United defence time and again, Olivier Giroud's header over the bar the closest they came.
There was even time for Louis van Gaal to amuse the home crowd as he dived to the ground as he remonstrated with the fourth official late on after Arsenal had been awarded what he perceived to be a soft free-kick.
While the result was a big blow to Arsenal's title challenge, Van Gaal's side are now just three points behind Manchester City in the final Champions League spot.
Manchester United: De Gea (7), Varela (7), Carrick (6), Blind (6), Rojo (6), Schneiderlin (6), Herrera (7), Mata (7), Depay (7), Lingard (6), Rashford (8).
Subs used: Fosu-Mensah (6), Januzaj (5), Weir (5).
Arsenal: Cech (6), Bellerin (6), Gabriel (6), Koscielny (6), Monreal (6), Coquelin (5), Ramsey (5), Welbeck (7), Ozil (7), Sanchez (6), Walcott (4).
Subs used: Giroud (5), Elneny (5), Iwobi (5).
Man of the match: Marcus Rashford