"It is nice to open the first two days of the tournament with two wins," Mittelstadt said.
The victory marked the second-straight win for USA White as they beat Finland to open the showcase on Saturday.
"Starting off 2-0 is definitely good for us as a group," Mittelstadt said. "However, while we came out with a victory today, we had some stretches where we did not play our best. But our goalie helped bailed us out."
American goaltender Dylan St. Cyr, who is eligible for the 2018 NHL Draft, made 27 saves in the crease.
Davidsson, Buffalo's second-round selection (37th overall) in the 2017 NHL Draft, had one shot on goal and recorded an assist in the loss.
"Marcus is one of the guys on our team with some experience playing here as he was here last year," Swedish head coach Tomas Monten said. "While he did not make the roster for World Juniors last year, he is a much more experienced player this summer.
"He is a player who can play on the wing or center but regardless where he plays, he can play a quick two-way forward game. He is a very hard worker with a lot of speed."
Davidsson and Mittelstadt were quick to praise each other's talents after the game.
"Casey is very smart, quick player who is a good skater," Davidsson said. "He plays a really good-fundamental game and he is a tough player to play against."
Mittelstadt said that he got to know Davidsson a little bit better during the Sabres' development camp in Buffalo earlier this month.
"While it was good to play against him in a competitive setting today, I am excited to see what the future holds for us moving forward," he said.
In Sunday's early game, Ukko-Pekka Luukkonen (2017, second round) served as the backup goaltender during Finland's 4-1 loss to Team USA Blue. The netminder will resume his duties on Wednesday when Team Finland takes on Team Canada at 1 p.m. at USA Hockey Arena.
The summer showcase has a scheduled off day on Monday, but resumes on Tuesday when USA White welcomes Team Canada Red to USA Hockey Arena for a 4 p.m. contest. USA Blue will faceoff with Canada White at 7 p.m.
Cliff Pu, (2016, third round), will make his debut on Tuesday when Canada Red faces USA White at 4 p.m. at USA Hockey Arena.