Nelson won it when he redirected a feed in the right circle from Martin Necas at the far goal post. It was Nelson’s 32nd goal of the season.
Gabriel Landeskog scored in his return from a lower-body injury, and Nicolas Roy also had a goal for the Avalanche (46-13-10). Necas had two assists, and Mackenzie Blackwood made 20 saves.
Alex Ovechkin tied it in the third period with his 1000th NHL goal (regular season and Stanley Cup Playoffs combined) for the Capitals (35-27-9), who have points in five straight games (3-0-2). Logan Thompson made 21 saves.
Ovechkin made it 2-2 at 14:17 with a power-play goal on a one-timer from the left face-off dot. He has 923 goals in the regular season and 77 in the playoffs, joining Wayne Gretzky (1,016) as the only players in NHL history to score 1,000 combined career goals.
Justin Sourdif gave Washington a 1-0 lead at 11:53 of the first period. Connor McMichael lifted an outlet pass into the offensive zone, and Sourdif got to it behind the defense and beat Blackwood with a wrist shot glove-side.
Landeskog, who missed seven games, tied it 1-1 at 1:05 of the third. Thompson went behind the net to play the puck and had his pass intercepted by Necas, who passed across the crease to Landeskog for a shot into the open net.
Roy gave Colorado a 2-1 lead at 6:03 when he forced a turnover by defenseman Cole Hutson and beat Thompson with a snap shot from the slot.
Capitals forward Ethen Frank left the game in the first because of a lower body injury after he was shoved on the rush by Avalanche defenseman Devon Toews and crashed hard into the net.