Washington forward Alex Ovechkin had his eight-game point streak end and remained two goals from tying Brett Hull (741) for fourth on the NHL goals list.
Brett Leason scored his first NHL goal, and Vitek Vanecek made 23 saves for the Capitals (5-1-3).
"It's frustrating. That's our team, we set the bar high," Washington center Lars Eller said. "There's no excuses. We hate losing, and it's an empty feeling for us right now. ... [Tampa Bay is] one of the best teams in the League. Tough challenge for us, and at the end of the day, we didn't get two points, but lots of positives also, Leason getting his first goal and stuff."
Anthony Cirelli had a goal and two assists for the Lightning (5-3-1), who have won three in a row. Andrei Vasilevskiy made 31 saves, including a sprawling glove save on Tom Wilson 17 seconds into the second period.
"You just don't want to be in positions to chase games, and he prevented us from doing that," Tampa Bay coach Jon Cooper said of Vasilevskiy's performance. "We scored right after that. Instead of it being 2-0, it's 1-1, and it's all because of the timeliness of that save."