Kevin Allen

USA TODAY Sports

NASHVILLE — The biggest reason the NHL’s new overtime format this season has been such a success is simple: Coaches haven’t figured out how to control it.

Most of them are masters at stifling the offensive magic of top players while building stout defensive systems. But those same coaches haven’t been able to unlock the key to three-skaters-a-side play that has been exciting and fast-paced and again will be on display in Sunday’s All-Star Game.

“We know the losing strategy,” St. Louis Blues coach Ken Hitchcock said. “You have to play the opposite of the way you would play four-on-four or five-on-five. If you get trapped ... playing like you do four-on-four or five-on-five, you will get scored on every time.”

Going into the All-Star break, 64% of overtime games (109 of 171) had been decided before the end of the five-minute period, which is then followed by a shootout to determine the game’s winner. A year ago, when even-strength overtime was played with four skaters on each side, 44% of the games were decided in overtime.

The rule change has had its desired effect, cutting down the number of games determined by a shootout and turning overtime into a highly competitive form of pond hockey. The three-on-three game has been such a success, the league adopted it for the All-Star Game, with each of the four divisions fielding a team in a tournament-style format.

“This is one of the best in­novations we’ve added to our game,” Nashville Predators general manager David Poile told USA TODAY Sports.

“It’s been exciting for the fans,” Detroit Red Wings winger Justin Abdelkader said. “Fans stand up for the whole five minutes. It’s end-to-end action.”

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Teams have studied what does and doesn’t work in three-on-three. A poor line change, gassed defenders or a missed shot that rings around the boards often can determine who scores first. And then there is the fact most players didn’t have much experience playing three-on-three before this season.

But it wasn’t always that way. Until 1985-86, three-on-three play in regulation was a semi-­regular occurrence when teams were assessed coincidental minor penalties while already each down a player. However, the high-powered and slick-skating Edmonton Oilers of the 1980s dominated opponents during the wide-open play, and the Wayne Gretzky rule was instituted, stating substitutions would be allowed on coincidental minor penalties. (The rule was amended more than a decade later to allow four-on-four play.)

“The biggest thing: You want the puck, and you want to keep it,” Washington Capitals coach Barry Trotz said. “If you have tired people on the ice against you, you want to keep them there.”

With so much open ice, teams can possess the puck for longer periods than in regulation and often tire out opponents. “Fatigue is a factor,” Blues center David Backes said.

What bothers coaches most is that it seems impossible to keep overtime from becoming a series of odd-man breaks.

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“If you miss a chance and you shoot the puck on net and the save is made, it’s an odd-man rush the other way,” Backes said.

And a team that has a high-quality puck-moving goaltender is at an even bigger advantage.

“You have to have a different dynamic, a different thought process,” Hitchcock said. “It’s like players have had to relearn a new game.”

Hitchcock says the way to play overtime is almost 100% opposite the way he wants to play in regulation. Routine shots on goal can be far riskier in three-on-three. “If you do things you normally do, boom, odd-man rush. Break­away. In the net,” he said.

Before the season, there was plenty of joking about how the Pittsburgh Penguins might use Sidney Crosby, Evgeni Malkin and Phil Kessel in overtime or the Tampa Bay Lightning might use Ondrej Palat, Tyler Johnson and Nikita Kucherov together. But coaches have mostly avoided deploying three forwards at a time.

Backes calls two forwards and a defenseman the industry standard in overtime.

But several teams do use two defensemen and a forward with regularity. Trotz says he likes to start with two defensemen.

“It’s about puck possession,” he said. “If you don’t start with the puck, you want your best defender out there.”

It’s easy for Trotz to switch to two forwards if his team has the puck because two players can pass the puck back and forth while the third man switches.

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“But if you don’t have the puck and a young kid like (Red Wings rookie) Dylan Larkin is winding it up and they give him the puck at full speed,” Trotz said, “then it is probably a better chance if I have (defensemen) Karl Alzner or Matt Niskanen playing one-on-one against him than Alex Ovechkin trying to back up and defend against him.”

Coaches still haven’t fully had their say on three-on-three. Hitchcock says that every morning he and his staff watch the overtimes from around the league the previous night to figure out if there is more they can do to control what happens.

The three-on-three format obviously has favored the teams that have a skilled forward group. For example, the defending champion Chicago Blackhawks are 9-4 in overtime, and 2014-15 finalist Tampa Bay is 7-1-3. Meanwhile, the Nashville Predators, who have been offensively challenged this season, are 3-7-1.

But his team’s poor performance in OT doesn’t alter Poile’s belief that the new format has made the league more exciting.

“As a general manager, I’m nervous and excited at the same time when my team is in a three-on-three situation,” Poile says. “But as a fan who watches games on a nightly basis, I love it.”