Johnny Gaudreau and Dylan Larkin each scored two goals and Morgan Rielly scored one of five goals in the first for Team North America, which also defeated Team Europe 4-0 in Quebec City on Thursday.
"I think we all realize that a 7-4 isn't what we wanted," Ekblad said. "Defensively, neutral zone, we've got to take care of that. We realize we were sloppy at times. Definitely a good start, but our second and third periods in both games haven't been up to par."
Video: EUR@NAT: Gaudreau goes five-hole on second goal
John Gibson made 29 saves in his first start for the team comprised of players 23-and-younger from the United States and Canada.
"These young players have a lot of courage," Team North America coach Todd McLellan said. "They want to have fun and play that way. But I'm pretty sure if we get moving along in the tournament and give up four goals a night, we're not going to have success. For as fast as we are transitioning, sometimes when we turn the puck over, we're going so fast it's hard to get going back the other way."
Forward Marian Gaborik scored two second-period goals, including one with 45.7 seconds remaining to draw Team Europe within two at 5-3.
Team Europe coach Ralph Krueger shortened his bench in an effort to get back into the game.
"Well, first of all the effort of everybody increased, but more than anything, we showed more patience in our game. We made more patient offensive decisions with the puck," Krueger said. "You saw more control, we spent more time in the offensive zone, and the goals were a result of that work. That was hard, but also smart, and that's the kind of team we need to be."
Video: EUR@NAT: Ekblad beats Greiss five-hole to pad lead
Pierre-Edouard Bellemare scored for Team Europe at 8:55 of the first.
Team North America already led 3-0 by that point, and Rielly's goal on a shot from the left point went into the net off Team Europe defenseman Mark Streit at 10:22 to make it 4-1.
Team Europe goalie Thomas Greiss was then pulled. He made four saves on eight shots.
Jaroslav Halak, who made 17 saves on Thursday, replaced Greiss. Gaudreau got credit for his second goal in two games after a shot rebounded off the end boards and into the net off Halak to increase the lead to 5-1 with less than five minutes remaining in the first period.
Halak made 22 saves on 24 shots.
"It was tough for Thomas," Streit said. "A couple of unfortunate bounces and things like that happen, it's hockey. And the poor guy, usually in goal you couldn't really do anything, but the pucks were in the net and I guess that's why Ralph decided to change the momentum and Halak came in and played a (heck) of a game. But both goalies are really good goaltenders and they're going to be a big factor in the tournament."
Video: EUR@NAT: Gaborik scores from the face-off circle
Frans Nielsen drew Team Europe within 5-4 at 8:17 of the third period when he finished off a passing play with Mats Zuccarello and Roman Josi to shoot past Gibson when he drove the low slot.
Gaudreau restored Team North America's two-goal lead with his second goal of the game at 11:29. He cut across the goalmouth and scored his third goal in two games on a backhand between Halak's legs.
Larkin, who did not play Thursday, scored his second goal into an empty net with 14 seconds remaining.
The World Cup begins Sept. 17 at Air Canada Centre in Toronto.
Goal of the game: Larkin scored his first goal at 6:27 of the first period, 1:07 after Ekblad opened the scoring. Trailing on a Team North America 3-on-1, Larkin was not picked up by Nielsen and scored on a rebound in the slot.
Video: EUR@NAT: Larkin bangs in Trochek's rebound
Save of the game: Gibson sprawled to his right to make a save on Team Europe captain Anze Kopitar's shot from the left side with 36.7 seconds remaining to keep Team North America ahead by two.
Unsung moment of the game: When Team Europe desperately needed to stop the momentum by Team North America, forward Thomas Vanek did that, putting a puck toward the net. Vanek, who did not play Thursday, shot from behind the goal line in the right corner and the puck handcuffed Gibson. Pierre-Edouard Bellemare was on the spot to put it behind Gibson and give Team Europe its first goal a after a rough start.
Video: EUR@NAT: Bellemare gets Europe on the board
Highlight moment of the game: Team North America left wing Auston Matthews made the play that led to Ekblad scoring his first goal at 5:20. Chosen No. 1 by the Toronto Maple Leafs in the 2016 NHL Draft, Matthews cut across the goalmouth after receiving a pass from linemate Brandon Saad on the right side. Matthews, who turns 19 on Sept. 17, had the puck knocked off his stick, but it went right to Ekblad, who shot past Greiss for a 1-0 lead.
Video: EUR@NAT: Ekblad rips a slap shot past Greiss
They said it
"I think you just can't be satisfied. I mean, we got up 5-1, I understand that can be hard to stay in the game, but they're a great team so they're able to come back in those kind of games. But we did a good job of holding them off. Ultimately, you don't want to win, well, you want to win a 7-4 game, but you'd rather that game end up 5- 6-1, or -2, or something like that. You know, we can't be giving that much up." -- Team North America captain Connor McDavid
"I thought we had a pretty good start, but all of a sudden you're down by four. They had some shots, they had some zone time, but it seems like they got the bounces as well. I thought after that we kept our calm. We had a better structure in our game, we stayed calm, and we finally got into the game and scored a goal, and I think that the last 40 minutes we improved a lot and that's what we have to take into next game on Wednesday." -- Team Europe defenseman Mark Streit
"Those two are skilled guys, they can shoot the puck. They've got great shots, they're fast, they've got some great speed, it's just fun playing with them so hopefully we can build off of tonight. And I think we had some good quality chances throughout the game. We might want to shoot a little bit more at times instead of being a little too pretty, but I think we had some chances tonight and hopefully we can build off of that." -- Team North America left wing Johnny Gaudreau on playing on a line with McDavid and Jack Eichel
Video: EUR@NAT: Gaudreau banks in a bouncing puck off Halak
"I really thought after the pain of the first period that for the first time standing behind the team you felt like the group was coming together. The talk on the bench and the way the lines worked after we changed them, it just felt better, so I think some good things come out of this game with us forward and we continue to build." -- Team Europe coach Ralph Krueger
Need to know: Is McDavid in a slump? Team North America had 11 players score a point in the first period Sunday and McDavid was not one of them. He has no points despite his team scoring 11 goals in its two pretournament games against Team Europe.
"I'm sure you guys will say a bunch of stuff but ultimately it doesn't matter," McDavid said. "We've won twice and that's all that matters. We have areas in our team game that we need to clean up. Personally, not the kind of start you want to get off to, but it's two games into the year, why would I worry?"
Team Europe: A pretournament game Wednesday against Team Sweden at Verizon Center in Washington (7 p.m., ET; ESPN3, SN360, TVA Sports 2).
Team North America: A pretournament game Wednesday against Team Czech Republic at Consol Energy Center in Pittsburgh (3:30 p.m., ESPN3, Sportsnet, Sportsnet1, TVA Sports).