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"Well, we know how skilled they are," Bonino said. "We played probably one of the best periods you can play against them. We gave them a few shots on the power play at the end of the first, but for the most part didn't give them much."
T.J. Oshie scored two goals for the Capitals (10-8-1), who lost for the first time in three games.
"We didn't deserve to win," Capitals coach Barry Trotz said. "We weren't ready to go. In the first period, they won every puck battle, every puck race. They got back to the front of our net really quick. They were getting tips. They were just more determined than us in the first period. It was ugly."
Forsberg gave Nashville a 3-2 lead at 6:45 of the second period on a turnaround shot from the left circle. It was his ninth goal of the season.
"It's obviously a great achievement," Forsberg said. "When you came into the League, you were obviously dreaming about getting there. It wasn't the prettiest one, but we'll take it."
Craig Smith gave the Predators a 1-0 lead at 11:48 of the first period on a redirection from the slot. It was his sixth goal.