Joe Sakic had the other goal for the Avalanche (3-2-2) and Jose Theodore stopped 26 shots to continue the Senators' struggles at Scotiabank Place.
Dany Heatley, who set a franchise record with 50 goals last season, scored his first of the season in the third period to make a game of it, but Ottawa (2-4-0) dropped its fourth straight game at home.
The Senators have never lost four in a row on home ice to start a season - their previous worst start was an 0-3-1-0 mark in 2001-02 - and it's the first time the Senators have lost four in a row on home ice at any point since they dropped that many from March 21 to 28, 2002.
Martin Gerber finished with 34 saves for the Senators.
It was Colorado's first win in Ottawa since Jan. 9, 1997. The Avalanche had been 0-5-1 since then in its visits and 0-3-1 versus the Senators overall, last beating them on Dec. 3, 2001.
The Avalanche visited Toronto's Air Canada Centre a night earlier and walked out with a 4-1 victory.
Despite making 27 saves against the Maple Leafs, Peter Budaj was on the bench and Theodore, who saw plenty of the Senators during his time with the Montreal Canadiens, got the start.
He was trying to atone for a pair of losses in his previous two starts, including a poor performance in a 5-3 loss to Chicago on Monday night in which he gave up a couple of questionable goals.
At the other end, Gerber had watched Ray Emery play the Senators' last two games and hadn't started since losing 4-3 to the Buffalo Sabres on Oct. 7.
Ottawa also had off-season signing Joe Corvo, who suffered a fractured right foot while blocking a shot in a Sept. 22 exhibition game, making his debut on the blue-line.
The Senators had been shut out in two of their past three contests at Scotiabank Place - all losses - and gave the crowd of 17,728 little to cheer about.
Theodore turned aside all 10 shots he faced through the opening period and, while Gerber faced the same number, the Avalanche were slowly began to turn up the heat.
Colorado outshot Ottawa 20-7 in the second and Sakic broke the deadlock just past the midway point of the period, taking a pass from Andrew Brunette and beating Gerber from close range for his third goal of the season.
The Senators' struggling power play, which was an NHL-worst 1-for-30 entering the game, put Ottawa into a bigger hole when it allowed Richardson to pick up an errant pass in his own end and break back the other way, beating Gerber over the shoulder with a shot from the faceoff circle.
With the crowd booing Ottawa's top line of Heatley, Jason Spezza and Daniel Alfredsson for its ineffective play, Spezza found Heatley in the slot and he snapped a shot past Theodore to break up the shutout bid.
The Senators' power play finished 0-for-4 while the Avalanche went 0-for-6.
Notes: Ottawa defenceman Wade Redden appeared in his 700th career game. It's the second most in Senators' history, trailing only Daniel Alfredsson's 712. . . . Defenceman Christoph Schubert and right-winger Brian McGrattan were healthy scratches for the Senators. . . . Ottawa is back in action on Saturday when New Jersey visits. . . . With Jordan Leopold (hernia), Brad May (shoulder), Cody McCormick (chest), George Parros (shoulder) and Pierre Turgeon (shoulder) all out injured, defenceman Kurt Sauer was the only member of the Avalanche to be scratched from the lineup. . . . Defenceman Karlis Skrastins' NHL-best consecutive games streak reached 440 straight contests. . . . Colorado wraps up its Canadian road trip Saturday at Montreal.