The £6m Mexican scored 20 goals in 45 appearances last season.
Little Pea, as his nickname translates, modestly said: "I'm not a symbol or an idol, or anything like that. Football is not a sport like golf but a team game. I am very motivated after a great season with Manchester United.
"From now on I'll owe a great debt to Sir Alex Ferguson for bringing me to Europe. My dream continues and has not changed. I want to win many titles to give back to the team that opened the doors for me."