Luukkonen made 18 saves, but took the loss.
"It felt pretty good to get out on the ice today," Luukkonen said. "We had a tune-up game back in Finland prior to coming to the United States so it is good to get back playing some competitive hockey games again. It was also good to play against Casey, but I would much rather be on his team after seeing him play today because he is a really good player."
In the second game of the 2017 World Junior Summer Showcase, Team Sweden played USA Blue and trailed twice by a pair of goals, but was able to eliminate both deficits in a 4-3 victory.
Davidsson, the Sabres' second-round selection in 2017 (37th overall), had a pair of shots in the win.
Cliff Pu, Buffalo's final prospect in the showcase (2016, third round), will make his debut on Tuesday when Team Canada Red takes on Team USA White at 4 p.m. at USA Hockey Arena.