The classy schemers started a game together for only the second time to help inspire a fabulous comeback, swapping positions and passing the ball with penetration and intelligence.
Kagawa, who performed superbly against Bayern Munich in his Borussia Dortmund days, could have played himself in contention for a starting role in the midweek Champions League encounter with Mata, who scored his first goal for the club, cup-tied.
"I think Mata is popular with the fans and the players because everyone can see what a good footballer he is," explained Moyes to MUTV. "I think he’s played well and really helped us and his goals were one of the reasons why we wanted to sign him.
"He’s always had a record of scoring goals and I thought he came very close against West Ham. There were signs that it was coming and, thankfully, he got his first today.
"I'm glad with Shinji. I thought he played very well at West Ham, too, but he made a very good pass to Juan for the penalty kick [on Saturday]. I want see more from Shinji in those moments because he's a very good footballer. He is technically gifted and can create good situations. It was also an excellent pass [for Wayne Rooney's header]."