The Union coach insists that the 21-year-old keeper's place remains secure despite the arrival of vastly experienced Oka Nikolav.
Despite doubts about MacMath, who has backstopped the second-leakiest defense in Major League Soccer's Eastern Conference this year, Hackworth insisted that Nikolav, who until signing with the Union had enjoyed a 22-year association with Eintracht Frankfurt, comes to the club primarily to play a mentorship role for the third-year keeper, not to take his job, and that his presence as a player is an ancillary benefit.
"Zac is absolutely, 100 percent still the starter," said Hackworth. "No question about that.
"The reality is that (Nikolav) is really coming here to be a mentor for our young goalkeepers. Both Zac and Chris [Konopka] are two guys that we believe very strongly in, but it's gonna help to have somebody with Oka's experience push to push those two players."
Hackworth also rejected the notion that his team's defensive record - the Union have allowed 24 goals, the second most in the Eastern Conference and are the only team in a playoff spot with a negative goal difference - is indicative of its overall quality or needs to be drastically changed.
"There's no question that we're a little thin on defense right now," he admitted, "but we like our defense, both that specific line - our back four - and our goalkeeper. We're young, we're going to have some inconsistent performances and some growing pains, but we like it. And that's one reason why [the selection] has been pretty consistent the whole way through."
He cited two matches - against Montreal and Los Angeles - where high-scoring games had inflated the overall tally.
"I think the goals against average can be skewed big time, especially the way we've played games. When you look at our game against LA [a 4-1 loss on May 15] and our game against Montreal [a 5-3 loss on May 25], you know those are games that opened up.
"As a coaching staff we could go into it and we can instruct the players, 'Hey, we're down a goal, let's just cut our losses and go home,' but we haven't done that at all. We keep going after it and we keep attacking, and that's not just a defensive thing, it's a team mentality, and I think you get a lot of positive out of that."