Sergachev turned 18 on June 25, the day after the first round of the draft. Born in Nizhnekamsk, Russia, he played his first season in North America with Windsor of the Ontario Hockey League in 2015-16. He had 57 points (17 goals, 40 assists) in 67 games and was the second rookie to win the Max Kaminsky Trophy as the top defenseman in the OHL.
He was the second defenseman selected in the draft, after Olli Juolevi went to the Vancouver Canucks at No. 5.
Sergachev has grasped the English language so well after such a short time living in Canada, Pacioretty is skeptical that it's only been a year since he left Russia.
"I told him, I don't even believe that," he said. "He hardly has an accent. I couldn't believe it when I heard that. It still sounds a little fishy to me."
Canadiens coach Michel Therrien appreciates Sergachev's high skill level, but said that is not why Montreal decided to keep him to start the season.
"There are a lot of 18-year-old kids who have talent," Therrien said. "With him, what we like is his maturity, he is physically strong, he understands the game. He has many things going for him. But we will take it one game at a time."
Sergachev is 6-foot-3, 215 pounds, so his body is NHL-ready. Canadiens assistant coach Jean-Jacques Daigneault, who handles the defensemen, called him "the total package" and said Sergachev already knows how to effectively use his strength at this level.
"I don't think his game is really knocking people over," Daigneault said. "I think Sergachev will do that, but it's not really his game. What we saw thus far in training camp is he's able to take people out just by sheer strength, but he's doing it the smart way. So he has good size, but he's using it properly."
The Canadiens also announced Monday that rookie left wing Artturi Lehkonen, 21, will be on the season-opening roster and that forward Michael McCarron, the No. 25 pick in the 2013 draft, was assigned to St. John's of the American Hockey League.