Jake Guentzel's grocery carts were filled with signs of his commitment to live like a pro.

"He'd buy stuff that my wife and I would never think of buying," Mike Guentzel said of his son, the Pittsburgh Penguins' left wing.

From organic beef and eggs to coconut oil and Himalayan salts, Guentzel went to the store last summer and filled his cart with only the right fuel for a body that now understood the toll the NHL's 82-game grind takes and why proper nutrition is one of the keys to surviving and thriving.

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He'd then go home and cook most of his meals on his own, so he knew exactly what and how much of it was going into his body.

It was quite a change for a player who last season lived alone and got used to making near daily runs to Chipotle because it was convenient.

"I lived right above one, so it was every night almost," Guentzel said. "Just the way I eat is the biggest thing now. I'm also getting more sleep."

Guentzel doesn't live alone anymore. His older brother Ryan and his girlfriend Natalie moved in with him, helping to continue to foster a lifestyle change that has been paying off in a massive way for the Penguins, who begin the 2019 Stanley Cup Playoffs against the New York Islanders at Nassau Coliseum on Wednesday (7:30 p.m. ET; NBCSN, CBC, TVAS).

The 24-year-old led them with 40 goals playing primarily on a line with Sidney Crosby after scoring 22 last season.

Video: DET@PIT: Guentzel cashes in on one-timer

"The biggest difference between Jake's year this year and years past is he's made a concerted effort to control all the controllables to give himself the best chance to be successful," Penguins coach Mike Sullivan said. "He's controlling his diet. He's controlling his rest. He's controlling his fitness level with his work habits off the ice and on the ice. He's worked extremely hard and I think because of that it's translated into consistency. We all know he's a real talented player and he has great chemistry with Crosby, but Jake deserves a lot of credit."

*****

Guentzel scored 13 goals and helped the Penguins win the Stanley Cup in 2017. It was a dream.

Waking up wasn't easy.

"Reality sets in," said his dad, a longtime college assistant coach and current pro scout for the Arizona Coyotes.

The reality of having to do it again, only now through a full NHL season after a short summer of celebrating. The reality of having to thrive in the face of rising expectations, of needing to prove you're not a one-hit wonder, that you deserve to stay in the NHL.

It's a daunting challenge even when you've experienced success like Guentzel had.

The challenge was getting the best of Guentzel in the middle of last season, when he slogged through a 28-game stretch from Dec. 7-Feb. 11 with eight points (four goals, four assists). His ice time tumbled from 18:30 in December to 13:32 in January. He played a season-low 9:01 in a 4-1 win at the St. Louis Blues on Feb. 11, 2018.

"Jake started on the first line," said Mike, who was in the building that night as part of the Penguins' dads' trip. "By the second period he was on the third line and by the third period he was on the fourth line. All of a sudden the big talk was 'Jake Guentzel is off the power play, Jake Guentzel might be a scratch in the next game.'"

Sullivan didn't go the distance. He instead met with Guentzel one-on-one.

The coach talked. The player listened. The message was delivered. It was crystal clear.

"I don't think I was bringing it every night and doing what I needed to do to be at this level," Guentzel said. "That meeting really opened my eyes up and made me realize that I have to buckle down here, or you never know what could happen."

The next night, Guentzel scored two goals and played 16:56 in a 6-3 win against the Ottawa Senators.

"In warm-up, he was on the third line and that was a good thing," Mike said. "Then he was on the power play. And then he scored. Then he scored again. He was playing with Sidney Crosby by the end of the night. Message received."

*****

Part of Guentzel's success is unquestionably because he plays with Crosby, who had assists on 25 of Guentzel's 40 goals this season.

"You know what, though, in order to play with good players and to be able to produce at that level, you have to be able to think it," Penguins assistant general manager Bill Guerin said. "It's not always easy playing with an elite guy."

It's not hard for Guentzel because, Guerin said, he thinks the game like Crosby.

Video: NYR@PIT: Guentzel connects with Crosby for goal

"Sid has played with a lot of other guys that haven't done what Jake has done to this point, but Jake's hockey sense is off the charts," Guerin said. "He thinks one step ahead.

"Every player that's ever played wants a 40-year-old brain and 20-year-old legs. Jake has 24-year-old legs and a superior hockey brain."

Mike Guentzel said his son developed his hockey sense as a kid, when he was a rink rat around his teams at the University of Minnesota. Jake was a stick boy when Penguins forward Phil Kessel played for the Gophers in 2005-06.

"He had skating ability when he first started and he had this ability to think it," Mike said. "I mean, you'd like to be able to think when you're around the kitchen table and your dad is a coach for as many years that you gain a certain level of hockey sense."

Hockey sense is why the Penguins selected Guentzel in the third round (No. 77) of the 2013 NHL Draft.

"He was the smartest player in the game every game I watched him play, and then he was also the most competitive," said Scott Bell, the former Penguins Minnesota-based scout who discovered Guentzel. "He just made play after play after play. Kids have certain decisions they can make and when you're sitting in the press box you can see all their options, and every time I would see the play, he'd make that play. Every time."

Guentzel wasn't much to look at that time. He was 5-foot-7, maybe 150 pounds with wispy blonde hair. He wore a white t-shirt when Bell met with him in Sioux City, Iowa prior to the draft. Bell, now a scout for the Toronto Maple Leafs, said he looked like a ninth grader.

"I told him when he interviews with any other team, wear a sweatshirt," Bell said, laughing.

Guentzel could think the game like a veteran, though. Penguins scouts even had conversations then about how one day he might grow up to play on Crosby's wing because of his hockey sense.

"We did in the sense that we believed he had high end ability and IQ," said Randy Sexton, the Penguins co-director of amateur scouting in 2013 and now assistant GM of the Buffalo Sabres. "We did believe that if he was able to grow to some degree and add the strength that we had a very talented offensive player on our hands."

Six years later, the Penguins have a goal scorer with a strict diet and a center who loves playing with him.

"He's just done a really good job of executing and finding different ways to score," Crosby said. "That's the challenge. Teams aren't going to be caught off guard by him. If you've got that many goals they're going to try to find ways to stop you, and he's found a way to get around that."