The Sweden defenseman had one of the greatest moments of his young life here six months ago, and he's hoping to have another one early next week.
On June 21, the Ottawa Senators made Karlsson the 15th pick of the 2008 Entry Draft, held at Scotiabank Place. On Friday, he walked back into the building for the first time since that night and took his first turns on the ice he hopes to make his second home in the not-too-distant future.
"For me it's a little bit extra (motivation)," he told NHL.com following Sweden's practice. "I like it here. It's good."
It's also felt good for one of his teammates, Andre Petersson, the Senators' fourth-round pick (No. 109) last June.
"Of course it's more special," Petersson said. "You have the eyes on you, you have the pressure on you … you want to impress the fans here."
Both players certainly have done that. Petersson, a 5-foot-9, 169-pound forward, is tied for the team lead with 3 goals and 6 points. Karlsson (5-11, 165) is tied for third among the tournament's defensemen with 6 points.
Sweden coach Par Marts said of Karlsson: "He's wonderful with the puck. You can't find a better offensive defenseman in this tournament."
With Scotiabank Place set up for hockey, the building looks far different to Karlsson than it did on that June night, but he remembers some things pretty vividly.
"I had to ask where the stage was, so then I remembered where I sat," he said. "It was a big night for me. I don't remember too much, I was a bit nervous. I remember when Ottawa picked me and that's it."
Senators fans watching the 2009 World Junior Championship certainly won't forget him.
Man in the middle -- One of the things to watch when the World Juniors started was watching Nikita Filatov shifting from left wing to center for Russia.
But it's been a partial experiment, as Filatov has moved from the middle to the wing and back throughout the tournament.
Columbus brass is hoping that Filatov can become the top-line center the Blue Jackets have lacked throughout the franchise's existence.
Filatov played center growing up, but for the most part he's been on the wing. Either spot is OK by him.
"I just need a little more time to be working in the center," Filatov said. "I used to play center. … I know how to do it. … I feel OK playing in the center, I just need more time to learn how to play there better. I'm OK to play center."
Good news for Canada -- X-rays on the right ankle of Team Canada forward Zach Boychuk reported only positive news.
Boychuk, who had 4 goals and 7 points in the first four games of the tournament, was crushed into the end boards by U.S. defenseman Teddy Ruth late in Wednesday's preliminary-round game.
Boychuk limped off the ice and left Scotiabank Place on crutches, but the swelling in his ankle went down considerably Thursday, and Boychuk hopes to play Saturday in Canada's semifinal game, against Russia.
"I think it's pretty much a go for tomorrow," Boychuk told reporters following Friday's skate. "I'm going to try it again (Saturday) morning and I should be ready to play."
Canada also announced Dustin Tokarski would start in goal Saturday in their semifinal against Russia. Tokarski had a slow start in his last game against the U.S., but settled down to make some very strong saves over the final 2 1/2 periods.
Start the party -- The hooting and hollering could be heard long after the game ended. But for Slovakia, this wasn't just any hockey game.
"I think it was one of the biggest moments in Slovakian history," said goalie Jaroslav Janus, who stole the game with 44 saves on 47 shots.
The game was televised live at home, where it's six hours later than Ottawa. And what a show they got.
Janus didn't think his team had much going for it -- when asked what he thought his team's chances were of beating the U.S., he said, "Not big."
"The U.S. almost beat Canada," he added. "We're going to play defensively, see how many goals we score. We got five goals, that's a lot against the Americans. I made some saves and we won the game."
Next for Slovakia is Sunday's semifinal against Sweden, which beat Slovakia 3-1 in group play. Can the underdogs -- who have become a Canadian crowd favorite -- pull another shocker?
"I think so," said Janus. "We can beat them tomorrow, but we have to play like today, then everything will be good."
Going home empty -- Team USA had high hopes coming into the tournament. But after Friday's shocking 5-3 loss to Slovakia, the best the Americans can hope for is fifth place.
The U.S. finished fourth last year but went undefeated in group play. And with the core of that team -- Colin Wilson, James van Riemsdyk and Jordan Schroeder among them -- back this year, big things were expected.
"It's quite a bit more disappointing going out in an earlier round," Wilson said. "We were more expected to win the whole tourney so it is more disappointing.
"I had a lot of confidence in the team. We were all trying to keep our heads up high. We just were a little snakebitten. Their goalie was hot and it gave them a lot of confidence.
"We're all disappointed, but that's just the way it goes."
The U.S. will play the Czech Republic on Sunday (7:30 p.m. ET, NHL Network).
Simple plan -- So how will Russia beat Canada on Saturday in the World Juniors semifinals?
Very simply, Russian captain Nikita Filatov said.
"Just have to score one puck more than Canada," he said.
Canada has beaten Russia in the gold-medal game three of the last four years, but there's no revenge on the mind of Filatov or any of his teammates.
"The guys here don't care about it," he said. "We were not there."
Contact Adam Kimelman at email@example.com.