The Blues continue to pile up the wins and points on home ice.
Semyon Varlamov made a career-high 41 saves in his first start since January 31 at Edmonton, but the Colorado netminder couldn't turn away Patrik Berglund's wrister from just inside the blue line that was redirected in the high slot by Colaiacovo.
"I had a lot of chances tonight. I've been getting a lot of chances lately. I'm just happy that one finally went in and it didn't take my stick to put it in," said Colaiacovo, who admitted that he felt the puck glance off his elbow.
Brian Elliott stopped 17 shots for St. Louis, which extended its franchise- record home point streak to 18 games (15-0-3). The Blues improved to 23-3-4 as the host this season.
The Avalanche had won two in a row, including a dramatic win against Carolina on Friday as Ryan O'Reilly scored with 1.2 seconds left in overtime.
Saturday's loss was the sixth in eight games for Colorado.
David Van Der Gulik won a faceoff back to Shane O'Brien and the veteran defenseman beat Elliott with a slap shot from the left point at the 10-minute mark.
David Perron, though, gave the Blues the lead with consecutive power-play goals.
The Avalanche had killed off 13 straight penalties, but that streak ended when Perron swept the puck through Varlamov at the left post at 12:12. He struck again 4:05 later, this time on a two-man advantage.
But Colorado demonstrated the effectiveness of its power play, tying the game on Erik Johnson's one-timer off a feed from O'Reilly with 50.2 seconds remaining.
It was the first power-play opportunity for the Avalanche in 164-plus minutes after their previous two opponents (Carolina and Chicago) were not whistled for a single infraction.
Milan Hejduk matched Adam Foote (967) for the second-most games played in Avalanche/Nordiques history. Joe Sakic is the franchise leader with 1,378...T.J. Oshie assisted on both of Perron goals...The teams split the four-game season series, with the home team going undefeated...Colorado has lost three straight in St. Louis for the first time since November 2, 2006- October 12, 2007...Colorado opened a four-game road trip on Saturday.