The 28-year-old bagged his second Premier League hat-trick as Palace recovered from going behind twice to claim a point against Bournemouth.
However, the Frenchman should have wrapped up all three points for Palace when Eddie Nketiah found him free at the penalty spot.
With only goalkeeper Djordje Petrovic to beat, Mateta blazed over the bar, much to the shock of all inside Selhurst Park.
Mateta had 11 shots against the Cherries, with 3.48 xG, but his 99th-minute chance equated to 16.38% of his xG.
The Palace striker has missed a league-high ten big chances this season but has still managed to score five goals in seven Premier League matches.
Eagles boss Glasner said an apology from Mateta was not necessary, explaining that he cannot expect his striker to convert every chance.
“He apologised,” said Glasner. “I told him there’s no need to apologise as you can’t take every single chance.
“He could have scored five or six because he had two big chances in the first half, but we don’t expect him to take every chance.
“He scored three, he has to be proud. It’s a hat-trick in the Premier League, which is not easy, but he did it and deserved it.
“When we see the goals, this is what we did better in the second half. I thought we played well in two-thirds of the pitch in the first half.
“We broke the press quite well, the sixes worked quite hard, but we were not direct and ruthless enough.
“We didn’t have the intensity to run in the box, we didn’t get the balls and the crosses were a little half. We needed more aggressiveness in their box.
“That’s exactly how the goals happened. JP had this feeling, which you hope your number nine has.
“He scored a very similar goal for France on the far post, he has this feeling.
“I’m usually very critical, but the players deserve huge credit for everything except our defending the third goal.”