Pogba's third-minute spot-kick settled the hosts' nerves as United allayed some of the doom and gloom predicted by Mourinho after failing to land a series of targets before Thursday's transfer deadline.
After a week in which Pogba has been linked with a move away from Old Trafford, with Barcelona's interest piqued by the Frenchman's frosty relationship with Mourinho after he was repeatedly dropped last season, the Portuguese showed his faith in the midfielder by surprisingly handing him the armband.
Mourinho has consistently complained in recent weeks over his lack of backing from the United board and also had a host of injuries and players lacking match sharpness after the World Cup to contend with.
Pogba resisted the pleas of Sanchez to take the spot-kick and after a prolonged stuttering run up, dispatched his shot into the top corner giving Kasper Schmeichel no chance to repeat his penalty saving heroics at the World Cup for Denmark.
However, he can still rely on one of the world's best goalkeepers as David de Gea put his poor World Cup showing behind him with a fine save to prevent Maddison levelling.
Fred had a debut to forget before being replaced 15 minutes from time and was lucky to even last that long when Mariner looked leniently on a kick out at Demarai Gray before half-time.
Both sides' top scorers from last season, Romelu Lukaku and Vardy, started on the bench after their World Cup exertions and were introduced for the final quarter.
Vardy nearly made a vital contribution as provider when he outmuscled Shaw and picked out Gray in the middle who was denied by another fine save by De Gea.
Lukaku then passed up a golden chance when Schmeichel spread himself well to turn the Belgian's effort over the bar.
Shaw, who himself has suffered plenty of criticism from Mourinho in the past two seasons, appeared to make the game safe when he fired low into the far corner to spark wild celebrations from his manager.
However, Vardy pulled a goal back deep into stoppage time when he stooped to head in after Ricardo Pereira's cross came back off the post and United were forced to see out a nervy final few minutes to get off to a winning start.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)