The injured Romelu Lukaku missed the 2-1 win at Bournemouth on Saturday and Marcus Rashford started on the bench as Jose Mourinho opted for a three-man forward line, with Anthony Martial and Juan Mata deployed either side of Sanchez.
The former Arsenal man was instrumental in United's first-half equaliser, setting up Martial, and will be disappointed to have been substituted towards the end of the game.
The match, won by substitute Rashford in injury time, was a rare high point for the Chile international, who has struggled to find his feet since arriving at Old Trafford in January — it was his first league start since September 22.
Following the much-needed win against Bournemouth, Mourinho praised Sanchez and spelt out his preferred system, saying he did not need a traditional centre-forward to lead his attack.
Klopp faces quandary over Fabinho
"The way I like to play is with three attacking players where there is not a clear definition of the winger as a winger," he said, adding that he likes wide men with a striker's appetite. "And I always had that in my team, with the wingers scoring a lot of goals, sometimes even more goals than the striker. So it's not impossible at all to have in the same team at the same time Rashford, Lukaku, Alexis for example. But today Romelu was not available and we thought that Alexis could do what he did.
"What he did, he had a good assist, he had some mobility, he created some problems but then in the second half I knew that by having the two brothers on the bench, Rashford and (Jesse) Lingard, I knew that the brothers could come in and also make an impact,” he added.
United now travel to Juventus for another date with former favourite son Cristiano Ronaldo, two weeks after they were outplayed during a 1-0 defeat at Old Trafford that left them five points adrift of the Italian champions in Group H.
Fernandinho the glue binding City together
Among a dazzling array of midfield options, it is the often unheralded Fernandinho who Manchester City manager Pep Guardiola has relied on most in another stunning start to the season for the Premier League champions.
The Brazilian will face old club Shakhtar Donetsk on Wednesday as City seek to make amends from the only blip of their campaign so far, a shock 2-1 defeat to Lyon in their last Champions League home game.
Guardiola urges Citizens to stay focused
If any reminder was needed over Guardiola's influence, he was banned from the touchline that night.
Since his return, City have won nine and drawn one, a 0-0 stalemate away to Liverpool, of their last 10 games, scoring 29 goals and conceding just two in the process.
Although fulsome in his praise of the maturing centre-back pairing Aymeric Laporte and John Stones, Guardiola's defensive philosophy is dependent on a team effort to keep the ball as far away from City's goal as possible.
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