Stewart's power-play goal opened the scoring and he assisted on the third goal against the team that traded him to St. Louis in 2010-11. His second goal in three games and team-leading 18th overall came on the deflection of Jordan Leopold's shot from the point, giving the defenseman his first point in 13 games since joining the Blues in a trade deadline deal with Buffalo.
Colorado penalty killers had been 10 for 10 the previous four games, including three chances by the Blues on Sunday, but paid for Jamie McGinn's interference call.
Berglund got his first goal in eight games with a deflection on a power play early in the second, with Leopold gaining another assist. McDonald made it 3-0 with his first goal in seven games, keeping the puck in the zone and then charging to the net for a return pass from Vladimir Sobotka before converting on the backhand at 5:13.
Colorado got on the board with just its second shot of the second period. The Blues appeared to relax on a delayed tripping call to McDonald in the offensive zone and the Avalanche got an odd-man rush with McLeod beating Elliott with a high drive to the glove side at 15:13.
Prior to his goal spurt, McLeod totaled three assists in 24 games.
"I got bumped up to (Ryan) O'Reilly's line," McLeod said. "I guess you're going to get more chances playing with them, and I've just been going to the net and kind of getting rewarded."
NOTES: Blues D Barret Jackman did not play in the third period after taking a puck below an ankle blocking a shot in the second. Hitchcock said Jackman might not be ready to play Thursday against Calgary. ... The Blues were 1 for 24 on the power play the previous nine games and last scored more than one goal with the man advantage on Feb. 15 at Calgary. ... Avalanche D Erik Johnson, the No. 1 overall pick by the Blues in 2006, missed his fifth straight game with a hand injury.