Monahan had a goal in regulation time and the game-winner in a shootout to lead his Red team over the Whites 3-2 in a controlled scrimmage on Monday at the Centre Sportif Bell.
The real chance for players to show team management they deserve a spot on the world junior championship team will come this week when Canada plays exhibition games against Finland, Sweden and the United States in Lake Placid, N.Y.
"What's so neat about this process is we get to play three games against teams that we're going to be playing against in the tournament," said coach Brent Sutter. "It's an evaluation for those teams too.
"We'll have a better idea of where we're at after those three games, and then we'll know what our needs and wants are and start forming a team, to some degree."
The camp is the first step toward selecting a team to play at the world juniors Dec. 26 to Jan. 5 in Malmo, Sweden.
A lot will depend on how players perform in the first half of the regular season with their club teams, but the summer development camp is a chance to leave an impression.
"It's important when you leave here to have a feel for what your core group might be," said Sutter. "The unknown is which kids could be starting the season in the NHL, but you still move forward.
"You have to have a plan in place, and I'll certainly have that discussion with the coaching staff and the management staff and we'll come to a conclusion in December."
Sutter estimates there could be up to a dozen of the 37 players in camp who could start the season in the NHL, although some of them could also be sent back to their junior teams and be available for the world juniors.
Among them is Monahan, who was picked sixth overall in the draft by the Calgary Flames. General manager Jay Feaster, whose team is thin down the middle, has said the six-foot-two centre will be given a good chance to make the NHL club.
"That's my goal, so I'm going to do whatever I can, but it's not up to me," said Monahan.
The Ottawa 67s star was among those who stood out in the scrimmage along with linemates Bo Horvat of the London Knights and Curtis Lazar of the Edmonton Oil Kings.
Horvat slid a nifty pass across the crease to Monahan, who waited a split second and then roofed a shot over Saginaw goalie Jake Paterson for the opening goal.
Horvat gave the credit to Monahan.
"I saw him driving to the net and I just tried to get it over as quickly as I could, and put a little sauce on it to get it over the stick," said Horvat, picked ninth overall by the Vancouver Canucks. "He made a great delay, great shot and put it up in the top corner."
The game was divided into two, 30-minute halves, and another Flames' first-rounder, Emile Poirier of the Gatineau Olympiques, gave the Reds a two-goal lead early in the second half from a scramble in front of Montreal Canadiens' pick Zachary Fucale.
But then 16-year-old Connor McDavid went to work for the Whites.
First, the Erie Otters' centre scored on a penalty shot after he was slashed.
Then he picked up an assist as Guelph defenseman Matt Finn tied the game with a blast from the high slot.
"He's a very good hockey player," Horvat said of McDavid, the favourite to go first overall in the 2015 draft. "I'm rooming with him here in Montreal and he's a great kid on and off the ice.
"He has tremendous skill around the net. His quick thinking, quick hands and his ability to make plays is unbelievable for his age."
McDavid is widely considered the best prospect since Sidney Crosby, and Sutter said this week he will be given every chance to become one of the rare 16-year-olds to make the Canadian world junior team, following the likes of Crosby, Eric Lindros and Wayne Gretzky.
He didn't look out of place, and he put a sweet deke on Paterson to score on his penalty shot.
However, in the shootout, he was robbed by a lunging glove save by Winnipeg Jets prospect Eric Comrie.
The shootout went six rounds before Monahan finally scored, just after the White team's Sam Reinhart saw his shot hit the inside of a goalpost and stay out. The 17-year-old Reinhart, of the Kootenay Ice, is another "underage" player looking to make the team.
Both sides were given chances to play on the power play (and penalty killing), and the last few minutes of each half were played four-on-four to give management a chance to see players in every situation.
The three goalies in camp took turns playing for both teams.
Fucale, fresh from a Memorial Cup victory with Halifax, can't wait to be tested by international shooters in Lake Placid. Canada will play Finland on Wednesday, Sweden on Thursday and the U.S. on Saturday.
"It's fun to be part of the big stage like this," said Fucale. "The difference between the under-18 team and the junior team is huge.
"You feel it right away. The game today was really intense. I can't wait to go to Lake Placid and play against other countries."
The four players returning from the team that finished fourth at the last world juniors in Ufa, Russia, will not make the trip to Lake Placid because they don't need to be evaluated.
And there is a good chance that Nathan MacKinnon, Jonathan Drouin, Sam's older brother Griffin Reinhart and defenceman Morgan Rielly will be playing in the NHL next season.