Ole Gunnar Solskjaer's side looked to have held on against hard-working Saints on Monday, with Marcus Rashford and Anthony Martial turning things around after Stuart Armstrong's early opener.
But just as United prepared to jump from fifth to third, substitute Michael Obafemi prodded home at the death to secure Ralph Hasenhuttl's men a deserved 2-2 draw at an empty Old Trafford.
The late heart-breaker was a blow with three matches of the season remaining, but Matic knows United cannot afford to wallow in self-pity.
"It's very frustrating for us," he said. "We had some chances to kill the game for 3-1. We didn't use that. We have to say that we played against a very good team tonight, but I don't think that we allowed them to create some great chances".