Danny Rose equalised from the resulting free-kick which flew over everyone and deceived goalkeeper Matt Ingram.
Morgan put 10-man Wycombe in the lead once more from the penalty spot and they looked like they were heading for a surprise win until James Constable knocked the ball back to Mullins who drilled home a dramatic leveller.
"There's a few gloomy faces in our dressing room but you won't see one from me, I'm not down at all," Wilder said.
"It's a battling point for us. And it's a good start to the season with ten points from four games.
"We conceded at a bad time and I don't feel David (Hunt) really needs to dangle a leg out the way he did, but Dean's a clever player and if he's given that invitation, he's going to take it. And he struck the penalty very confidently.
"That goal gave them a lift. It disappointed me because we were massively on the front foot at that point, and there was still half an hour to go."
"At times Wycombe were a touch sharper than us and we didn't move them around enough when they had 10 men, or play with a quick enough tempo, but this game showed my team plays to the end. It might be a valuable goal come the end of the season.
"And yes, of course, there's relief as well.
"Credit too to Wycombe. They got spanked last week, but they scrapped and battled and gave their manager everything."