In the third period, however, the Sabres tested their luck one too many times. A call against Evander Kane for hooking gave the Capitals their third power play with 6:18 remaining in regulation, and it took only five seconds after that for Marcus Johansson to tie the game with a tip-in goal.
The game rolled into overtime, and Johansson - who also scored in the first meeting between the Sabres and Capitals - scored the game-winner midway through the extra period to seal a 3-2 victory for Washington.
"Their power play is dangerous," Sabres coach Dan Bylsma said. "I thought we did a good job of killing them off in the first period but the second goal, the goal that they needed there with six minutes left, was a direct result of the penalty kill. We had our chances on the power play … We weren't able to come up with it."
After Johansson scored to tie the game, the Sabres still earned one more power-play chance of their own with 3:12 remaining in regulation. Like their first two power plays, however, they failed to turn it into any momentum. The Sabres were outshot 4-3 combined on their three chances with the extra man.
"Our execution was kind of poor," Okposo said. "It just seemed like we weren't in sync, we just weren't making the play that we normally do. Next game I think we just have to bear down and make sure that we're back to being simple."
Even without success on the power play, the Sabres earned their lead during a hard-working second period in which they outshot the Capitals 16-7. Okposo's go-ahead goal in the second period capped off four shifts of relentless play around the Washington net.
The third period spurred opposite results, with Washington outshooting Buffalo 16-9.
"In the end, we're not winning hockey games with one good period," said Sabres goalie Robin Lehner, who made 30 saves. "We see that we can play, so we've just got to stop changing how we play."
The loss marks the second in a row the Sabres, who found little solace in taking a point on the road. They'll have one more chance at beating the Capitals when they meet again at KeyBank Center on Friday night.
"I think at this point we know that we need two [points] and we've got to try and fight our way up the standings," Okposo said. "You're going to have some lulls in a season but we already had ours and we have to make sure that we're pushing forward and doing everything that we can to get two points. Yeah, getting a point is OK, but we had the lead in the third. We've got to try and hold it and get two."