Martial brought the game back level after Emmanuel Bonaventure made in 1-0 to Brugge.
Mata told MUTV after the game: "If you want one player to go against the goalkeeper, he's one of the best in our team for sure.
"He was very calm, very composed, great finish and a very important away goal."
The draw means United go into the return leg at Old Trafford next Thursday with an away goal, meaning Brugge will likely need to win in order to progress.
Martial's goal was his second this week after he put United ahead in their 2-0 win over Chelsea on Monday night.