United raced into a two-goal lead at Stamford Bridge but were pegged back as Roberto Di Matteo’s side launched an impressive comeback to draw level in the second half.
However, after Branislav Ivanovic and Fernando Torres were both given their marching orders, the Mexican grabbed a late winner which he believes could prove vital come the end of the season.
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"That's why it was important we didn't allow them to get ahead. It was vital to get the three points at a very tough place. We are in there in the fight to win [the Premier League]."
The 24-year-old's winner was one of many controversies during the match, as he appeared to be in an offside position before converting, but the former Guadalajara man intimated that he is just happy to have scored.
"I don't' care... the referee counted it," he continued.
"When Robin [van Persie] shot and [Petr] Cech made a great save I went for the rebound and the ball went to Rafael.
"The first thing was to get along the line of defenders because I thought that was where the ball was going to go. Thankfully I reacted well to it."