BROSSARD, Quebec -- This is not a simple, run-of-the-mill demotion.

Coaches shuffle players back and forth between forward lines and defense pairings every day.

But when Montreal Canadiens coach Michel Therrien decided to split his top defense pairing of P.K. Subban and Andrei Markov midway through the second period of a 3-1 loss to the San Jose Sharks on Tuesday, it was an important moment not only for this edition of the Canadiens, but potentially the entire organization for years to come.

Markov was dropped to the third pairing with Tom Gilbert and replaced on the top pair by Nathan Beaulieu, who for all intents and purposes is Markov's eventual replacement on the Canadiens depth chart on defense, one that has had Markov in the No. 1 or 2 spot practically his entire 15-season NHL career.

Those pairings remained in place at practice Wednesday and are expected be the same when the Canadiens host the Pacific Division-leading Los Angeles Kings at Bell Centre on Thursday (7:30 p.m. ET; CITYM, FS-W, RDS).

"I'm not looking for any excuses, I have to play better," Markov said Wednesday. "Many guys on our team have to play better. So we have to realize that and be better the next game."

Markov and Subban had a rough game against San Jose; Subban was caught up ice leading to a 2-on-1 break for the Sharks that ended with Patrick Marleau's opening goal, and Markov committed a bad giveaway that created a 2-on-0 in front on San Jose's third goal.

That was when Therrien decided to switch his pairings, which was not much of a surprise. The surprise was that they stayed intact at practice Wednesday.

"I didn't like the Markov-Subban pairing, so I decided to change it," Therrien said. "That's it."

However, that's not it when it comes to this decision. Far from it.

Here's why:

Father time

This will be the first time Markov has played on the Canadiens' third defense pairing in more than a decade. Aside from 2011-12 when he played 13 games between two knee injuries, Markov has not averaged fewer than 20 minutes of ice time per game since 2001-02, his second season in the NHL.

Therrien was asked Wednesday if doing this was difficult considering Markov's stature with the Canadiens is comparable to what Nicklas Lidstrom represented for the Detroit Red Wings; not comparing the quality of the player, but in terms of the position he has held on the team for as long as he has.

Therrien avoided the question, which basically confirmed the premise was true; this is difficult.

But it is also necessary.

Markov turns 37 on Sunday and is playing 22:54 per game, down exactly two minutes from last season, but still a significant amount for a player his age. Playing alongside Subban means those are difficult minutes, facing top opposition, killing penalties and playing the bulk of the power play.

Over the past two seasons, Markov's play has dipped significantly in the Stanley Cup Playoffs, and it is clear Therrien and his staff wanted to cut his ice time in order to keep him fresh for the postseason.

Now, playing with Gilbert on a third pair, Markov's minutes are sure to be cut even more, which might make him a better player in the spring if he continues to carry a lighter load.

That doesn't mean Markov necessarily has to like it.

"The coach is going to decide how many minutes I play," Markov said. "So I have no choice, I have to accept that."

Balance

Throughout Markov's career, he has made a habit of making whoever happens to be playing next to him better. Subban might have needed that support for a while, but he is now one of the top defensemen in the NHL and clearly doesn't anymore.

The beneficiary could be Gilbert, who has played well this season but might now see his game reach new levels with a legitimate top-pairing defensemen playing next to him against bottom-six opposition.

Gilbert and Markov began last season playing together before Therrien decided to pair Markov with Subban, so there's a history there, and Gilbert is eager to rekindle it.

"It was really easy playing with him last year, that's for sure," Gilbert said. "He makes the game really easy."

Heir apparent

Beaulieu, 23, is the player best-positioned to one day take over Markov's role as the Canadiens' top left-shooting defenseman. He's an excellent skater, imaginative playmaker and is becoming a sound defensive player, all traits he shares with Markov, though probably not yet at the same level.

"I'm ready for it," Beaulieu said. "I know playing with P.K. means more demanding minutes, tougher minutes. But I've been prepared for moments like this."

The Canadiens have to be prepared for it as well, which is what makes this move so important. It might just last one game, or even one period, but at some point Beaulieu will need to learn how to play those tough minutes with Subban, and Markov will need to accept that he needs to dial it back in order to remain effective.

The sooner the Canadiens get that process moving, the better off they will be.

Now is as good a time as any.