Mason blanked Detroit 5-0 on Jan. 28 and stopped the Los Angeles Kings 2-0 on Feb. 1. He was only 2:50 away from his fourth shutout of the season, and third in five games, when Nathan MacKinnon beat him for his 21st goal of the season. Mason stopped his first 33 shots.
Claude Giroux scored an empty-netter in the final minute for the Flyers.
The 25-year-old Mason signed $12.3 million, three-year extension last month, a deal already paying off big for the Flyers. He's been the key reason the Flyers have been able to hang around in the Eastern Conference playoff race.
The Avalanche, who lost 5-1 to the New York Rangers on Tuesday, couldn't solve Mason until it was too late.
The Avalanche called timeout with 1:27 left and pulled goalie Semyon Varlamov in a last-gasp effort at the tying goal. It didn't work.
The Flyers scored in the second period, when Streit's shot from the blue line was deflected by a defenseman and wobbled past Varlamov for his eighth goal.
"It's a big goal for us at the right moment," said Streit, who's heading to his fourth Olympics for Switzerland.
The Flyers got a scare when center Brayden Schenn was checked from behind into the boards by Patrick Bordeleau. Schenn quickly got on his skates, and his teammates went after Bordeleau behind the net. Bordeleau threw his right elbow into Schenn's back and the Flyer thumped the board, and then hit the ice.
Bordeleau was hit with 5 minutes for checking from behind and a game misconduct. Colorado coach Patrick Roy was red faced and furious as he argued with the officials that the hit didn't merit an ejection.
Mason's play picked up after a recent pep talk from Hall of Fame goalie Bernie Parent. Mason stopped 14 shots in the first period and made the save of the night in the second when he robbed Gabriel Landeskog with a glove save from his rear.
He posted a 1.51 goals-against-average over his last four starts, stopped 95 percent of his shots and had two shutouts.
Raffl's seventh goal of the season, off a nice pass by Sean Couturier from behind the net, early in the third was the insurance the Flyers needed to win their third straight.
The Flyers returned home Thursday after a three-game road trip that included wins against the Los Angeles Kings and San Jose Sharks.
Notes: The Flyers had a video tribute and a moment of silence for former coach and general manager Keith Allen. Allen died Tuesday. He was 90. "I love Keith Allen," Flyers founder and chairman Ed Snider said. ... Lauren Hart, the daughter of longtime former Flyers broadcaster Gene Hart, sang "God Bless America," alternating lyrics with Kate Smith, who was on a video image. Smith's rendition of the song has been a rallying anthem for the Flyers since the mid-1970s.