Despite United fighting back from three goals to secure a point, Mata had the chance to snatch victory for his side, only for De Gea to produce a contender for save of the season.
The Spanish goalkeeper endured a shaky start to his career at Old Trafford, but his performance in recent months have seen some tout him as a candidate for United’s player of the season.
The former Atletico Madrid shot-stopper has kept six clean sheets in his last seven games to help United establish a five point gap at the top of the table from rivals Manchester City, and he believes that it is possible to trace his change in fortunes this season back to the game at Stamford Bridge.
"When you look back over a season there are lots of defining moments and key goals," he told ManUtd.com
“But, I suppose, from a team point of view, and particularly from a personal point of view, the fact the save was right in the last minute was decisive.
"Possibly it gave me a huge confidence boost as well. From a personal perspective that was important."
De Gea also believes United's fans have played a vital role in helping to transform his fortunes.
“It is always a positive when the fans are behind you. It is something I can sense when I am out there on the field," he added.
"It always helps you feel more relaxed and it is a source of extra motivation when you know the fans are right behind you and rooting for you.
"But all that aside, it is just a case of getting your head down, keep working hard and making sure you do have a continuous improvement all the time."