Paul Stastny had a goal and an assist, T.J. Galiardi also scored, and Craig Anderson made 32 saves for the Avalanche. Colorado moved into a first-place tie with idle Vancouver in the Northwest Division.
Eric Brewer and Erik Johnson scored for the Blues, who have lost three in a row.
The Avalanche blew it open in the first 6 minutes, 34 seconds of the second period. With the game tied at 2, Colorado got goals from Stewart, Stastny and Yip 4:09 apart to take a 5-2 lead and chase Chris Mason, who allowed five goals on 15 shots.
Stewart's three points tied a career high, and his 18 goals tie him for the team lead with rookie Matt Duchene. It was Yip's third two-goal game this season, and gives him 11 goals in 22 games.
Anderson was briefly down on the ice in the second period after taking a puck in the upper chest on a shot by Andy McDonald. A Colorado trainer attended to him in the crease, but Anderson stayed in the game.
The Blues thought they had cut the lead to 5-3 when T.J. Oshie tipped in a rebound midway through the second period, but the goal was disallowed on a hooking penalty called on Oshie.
The game provided early excitement. Just 2:21 in St. Louis forward D.J. King dropped the gloves against David Koci, and the fight seemed to provide some spark. Brewer made it 1-0 with a wrist shot at 3:34 of the first, but 28 seconds later Galiardi tied it with a point-blank shot that beat Mason over his left shoulder.
St. Louis took a 2-1 lead when Johnson beat Anderson with a shot to the short side with 12:01 left in the first. Yip tied it on the power play with 3:18 left in the first period.
NOTES: Johnson's goal was his first since Nov. 30 at Columbus, a span of 31 games. ... Koci suffered a hand injury in his fight with King and did not return. ... Colorado C Ryan O'Reilly (bruised foot) missed his first game of the season. ... Conklin had 18 saves.