Rooney cheered and applauded the glut of United goals as enthusiastically as anybody as he sat on the bench but he may yet look back on this match as the beginning of the end of his time at Old Trafford. Rooney came on in the 83rd minute in place of one of the goal-scorers Rashford but that was hardly of any significance.
For the first 20 minutes it may have been more of the same from United - ponderous and slow in their approach - but once Smalling had headed in Daley Blind’s corner the shackles were released.
Mata, nominally playing in Rooney’s place behind Zlatan Ibrahimovic, was bright and lively and took his goal superbly before teeing up Rashford for a tap-in, but it was in midfield that the hosts were able to really take a grip of the game as Leicester froze.
United’s first-half performance was their best of the season so far, and went hand-in-hand with Pogba’s finest display since his world-record move to Old Trafford this summer.
Mourinho chose Ander Herrera to partner him instead of Marouane Fellaini or Michael Carrick, and Pogba played noticeably further forward, often interchanging with Mata. He had already played two searching cross-field passes before a flurry of individual highlights as United scored three goals in five dazzling minutes at the end of the first half.
Pogba delivered a disguised chip over the top to Ibrahimovic, who volleyed over, fired in a dipping 35-yarder that was well saved by Ron-Robert Zieler, and sliced through a pass that freed Antonio Valencia.
The Frenchman then played a key part in Mata’s second before he headed his first goal for the club.
United’s first Premier League win in a month was sealed by half-time, but a third defeat for Leicester already matches their total for the whole of last season.