The Chilean forward had been refused entry into the United States due to visa issues, but United's legal team worked on securing a waiver for their player.
Sanchez duly travelled to America on Friday evening and is involved from the off as Jose Mourinho's charges take on the Major League Soccer Western Conference side.
Mourinho has also given 17-year-old midfielder James Garner his first-team debut, while forward Tahith Chong is rewarded for his impressive cameo against Club America with a spot in the XI alongside Sanchez and Anthony Martial.
Antonio Valencia, Eric Bailly, Chris Smalling and Luke Shaw all start in a strong defence, while Joel Pereira features between the sticks and Andreas Pereira is given a start alongside Ander Herrera and Garner in midfield.
San Jose Earthquakes: Marcinkowski; Qwiberg, Cummings, Kashia, Lima; Hyka, Jungwirth, Felipe, Wehan; Amarikwa, Hoesen
Manchester United: J. Pereira; Valencia, Bailly, Smalling, Shaw; Herrera, Garner, A. Pereira; Chong, Martial, Sanchez
Subs: Grant, Darmian, Fosu-Mensah, Mitchell, Tuanzebe, Williams, Bohui, Gomes, Hamilton, McTominay, Mata, Greenwood
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