Vrana's one-timer from the right face-off circle made it 3-0 at 9:29.
"I just tried to find an empty spot there around the net, and it was a great pass by [Kempny], and I just tried to finish it off," Vrana said.
Boyd helped make it 4-0 when he skated behind Ullmark and sent a pass through the crease for Leipsic, who scored on a one-timer at 10:44.
The Sabres had several odd-man rushes late in the period but couldn't convert.
"We got away from the game, the simple game, and the decisions we needed to make with the puck," Buffalo coach Ralph Krueger said. "We gave them really everything they got in the first period, and we had some excellent opportunities that we didn't capitalize on."
Jokiharju's first NHL goal cut it to 4-1 at 10:40 of the second period when his shot from the left point deflected in off Washington defenseman Jonas Siegenthaler.
"Obviously, in that moment that was a feeling of happiness and it was fun to score, but after this kind of game, it's not that big [of a] memory right now, but probably a little bit later," Jokiharju said.