The Concord Township, Ohio native wrested the job from veteran Troy Perkins midway through the Impact's disastrous 2014 season and will keep the title despite the off-season acquisition of veteran Eric Kronberg from Kansas City.
"Eric is an experienced guy, which is good, because he can also help mentor Bush and the younger guys, but he's in a spot where he's pushing to compete," said coach Frank Klopas. "Evan is our No. 1 guy, but it's a competition. That's only fair."
Bush, who turns 29 on March 6, joined the Impact a year before they entered MLS in 2012 and was the top 'keeper in the NASL.
In MLS, he played only one league game in each of his first two seasons, playing first behind Donovan Ricketts and then behind Perkins. He got most of his work in Voyageurs Cup and reserve league matches.
But in Montreal's 17th game of the 2014 campaign, the midpoint of the 34-game schedule, a miscommunication between Perkins and defender Heath Pearce allowed Kansas City's Dom Dwyer to score the game-winner in the 89th minute of a match at Saputo Stadium.
It appeared that Klopas had seen enough because the next game, a 2-1 loss in Columbus, Bush was in goal for the first of 13 starts the rest of the way.
"We just had to see what we had there," said Klopas. "We had no chance to make the playoffs.
"He was training really well. You had to give him an opportunity."
Bush had been sharp as the team won back-to-back Canadian Championships in 2013 and 2014, which put Montreal into the CONCACAF Champions League.
Now he is the likely starter when Montreal starts play in 2015 against Pachuca in the quarter-finals Feb. 28 in Mexico and March 3 at Olympic Stadium.
"As far as training, it doesn't change," Bush said of the starting job. "Obviously, because we have a big game straight off the bat, we can't waste any time. But most things haven't changed."
He stayed patient in his time as a backup, but when his chance came, he felt he'd earned it.
"I'd been pushing (Perkins) in training for a long time," he said. "I thought there were a lot of days where, if you stacked us up against each other, I felt like I was just as good if not better on a lot of days of training.
"We started losing a lot of games last year and that was a change they made. The first few games, it was a bit shaky, but over the course of the next eight or 10 games I felt very strong."
Montreal let Perkins go at the end of the season, but then took Kronberg with the first pick in the re-entry draft. Kronberg was Kansas City's starter, playing 20 matches in 2014, until his season ended with a broken finger in July.
The 31-year-old gives Klopas an experienced backup if Bush falters or gets injured. The club has done much the same at nearly every position this season, creating internal competition for playing time that they hope will keep them sharper and stronger this season.
"You're always competing against whoever's at your position," said Bush. "Goalkeeper is unique because there's only one guy who can play.
"But you need to have a good working relationship with each other because otherwise, you won't get anything out of training."
Kronberg said: "We're both very good 'keepers and competition is healthy. We want to be pushing each other and making sure that whoever is playing is the best he can be."
Because Kronberg has already played in the 2014-'15 Champions League for Kansas City, he is ineligible to play for Montreal against Pachuca. And third-stringer Maxime Crepeau is out with a shoulder injury.
So the Impact acquired German goalie Kristian Nicht on loan from the NASL club Indy Eleven to serve as Bush's backup. The 32-year-old Nicht, to be with the club until March 4, trained with the Impact on Thursday.