United moved to within two points of fourth placed Arsenal as three goals in eight minutes despatched lacklustre champions Leicester.
Both the Gunners and Liverpool suffered away defeats and, for what seemed like the first time in ages, the Reds fully capitalised with a clinically emphatic performance.
After seeing a sequence of nine successive wins halted in frustrating fashion, this was a timely return to winning ways for Jose Mourinho's men, who extended their unbeaten league run to 15 matches - the longest of any side in Europe.
The result left Claudio Ranieri's side - who were a shadow of their title-winning selves - precariously perched in sixteenth place, one point above the relegation places.
The Reds started brightly and went close after five minutes when Marcos Rojo had a volley clawed away by Foxes keeper Kasper Schmeichel.
United monopolised possession but Leicester worked their way back into the match and almost equalised when Wes Morgan had a header deflected wide after Riyad Mahrez and Jamie Vardy had linked up well from a set piece.
Eric Bailly's brilliant lunging challenge prevented Ahmed Musa from getting one-on-one, and Rashford then should have done better at the other end when well placed.
The young striker was involved again soon afterwards, and this time forced a smart save from Schmeichel, who did well to tip Rashford's effort wide.
United ended the half on the front foot and moved ahead three minutes before the break.
Henrikh Mkhitaryan collected the ball on halfway from a Chris Smalling knockdown before he raced away from Robert Huth and ran through to rifle beyond the advancing keeper.
Leicester hadn't fully recovered their composure when the visitors struck again as Zlatan Ibrahimovic notched his 20th goal of the campaign.
Antonio Valencia burst clear down the right and cut the ball back to the lurking Ibra, who took a touch and slammed home from close range.
The champions were shell-shocked by United's quickfire double and registered their first and only shot on target in first half stoppage time when Wilfried Ndidi fired straight at David de Gea.
Untied continued on the front foot after the restart and put the result beyond any lingering doubt with the third goal on 48 minutes.
Juan Mata checked inside Christian Fuchs endplayed a lovely one-two with Mkhitaryan before he slotted home from a tight angle for his eighth of the season.
Rashford was denied by Schmeichel and Mata should have added a fourth, whilst the impressive Mkhitaryan lashed over the bar from close range after Valencia's cut-back.
That proved to be the final action of a dominant United performance, a result which left the struggling and beleaguered Foxes in a real battle for survival just months after their historic top flight title.
Overall team performance: 7.5/10
United Faithful Man of the Match: Henrikh Mkhitaryan