Ryan Stoa also had a goal and Kyle Quincy had two assists for the Avalanche, who won for the first time in three preseason games.
Richard Bachman had 28 saves for Dallas, which fell to 3-1 in the preseason.
The Avalanche scored their first goal on their first power-play of the game. Joakim Lindstrom took the puck at the point, maneuvered to find an open shooting lane and sent a shot to the front of the net. The puck bounced off Stoa at the top of the crease and trickled through the legs of Bachman, who was screened on the play.
Early in the second period, Gabriel Landeskog, the second overall pick in the June draft, carried the puck down the right side into the Dallas zone early and feathered a pass to O'Reilly, who had gotten behind the Stars' defense. O'Reilly lifted a shot over Bachman's right shoulder to give Colorado a 2-0 lead 2:24 into the frame.
O'Reilly banged home Quincy's rebound shot to make it 3-0 late in the period.
Giguere faced an early test when Dallas had a 5-on-3 power play for 1:22 just 73 seconds into the game. But Dallas managed just one shot on the two-man advantage and Giguere easily stopped it.
|PPG - Ryan Stoa (1) Deflected shot - ASST: Joakim Lindstrom (1), Kyle Quincey (1)|
1 - 0 COL
|Ryan O'Reilly (1) Wrist shot - ASST: Gabriel Landeskog (1), Stefan Elliott (1)|
2 - 0 COL
|Ryan O'Reilly (2) Snap shot - ASST: Kyle Quincey (2), Daniel Winnik (1)|
3 - 0 COL
|Power Play %||40.0%||100.0%|
|% on Road||0.0%||0.0%|
|% at Home||40.0%||100.0%|
|Paul Stastny Hi-sticking - 2 min against Tom Wandell|
|Jonas Holos Delaying Game-Puck over glass - 2 min|
|Travis Morin Hooking - 2 min against Matt Duchene|
|Kevin Porter Interference - 2 min against Mathieu Tousignant|
|Shane O'Brien Boarding - 2 min against Steve Ott|
|Krys Barch Fighting (maj) - 5 min against Patrick Bordeleau|
|Patrick Bordeleau Fighting (maj) - 5 min against Krys Barch|
|Joakim Lindstrom Unsportsmanlike conduct - 2 min against Philip Larsen|
|Nicklas Grossmann served by Ryan Garbutt Boarding - 2 min against Matt Duchene|
|Nicklas Grossmann Roughing - 2 min against Ryan Stoa|
|Ryan Stoa Roughing - 2 min against Nicklas Grossmann|
|Sheldon Souray Elbowing - 2 min against Ryan Stoa|