The 29-year-old forward was fully involved in United’s pre-season matches and completed 90 minutes in their Premier League opening 2-1 win against Leicester.
Sanchez was not mentioned by Jose Mourinho in Friday’s pre-match press conference but speculation mounted over the weekend, with reports that the Chilean had not flown to the south coast with his team-mates.
An hour before kick-off at the Amex Stadium, United revealed an 18-man squad that did not include Sanchez.
Speaking half an hour before the teams walked out, Mourinho told Sky Sports: “Honestly, Alexis was going to play but he had a little problem, so we had to decide the opportunity for one attacking players.”
Winger Anthony Martial, recently fined after leaving the US tour for the birth of his second child, was given a rare start.
Romelu Lukaku and Ashley Young, both recently returned after playing at the World Cup, were also in the starting XI, while Paul Pogba was made captain again in Antonio Valencia’s absence.
Asked about Martial’s inclusion, Mourinho added: “It’s an opportunity. I don’t want to say big opportunity.
“We know Anthony well, and we can always expect good things from him. Can he find that stability that makes the great players? We try, we try to help, and he’s working well.”