O'Connor made it 4-1 at 15:37 with a shorthanded breakaway off a Darren Helm pass.
Barabanov cut it to 4-2 at 9:02 of the third period with a shot from the left circle on a power play.
Andre Burakovsky put in a deflected shot from the right circle at 10:13 to make it 5-2.
Girard scored into an empty net at 16:37 for the 6-2 final.
"I thought he was great," Avalanche coach Jared Bednar said of Girard. "He was moving, jumping into the play. One of the best parts of his game, when the puck was moved up the ice to our forwards he was always getting into the right spot. He was a dangerous option off the rush and moving into the offensive zone. His best game that we've seen him play in a while."
Forward Timo Meier was among the Sharks players returning from COVID-19 protocol.
"It's nice to back, especially after that tough time," he said. "I think we started off well, we took a lot of penalties and it kind of takes away the momentum. I think overall we didn't work enough and we played sloppy. That's what cost us this game and made it an easy night for them."
NOTES:Avalanche forward J.T. Compher left the game after he sustained an upper-body injury in the first period. He was the center on the top line in injured Nathan MacKinnon's absence. "Upper body, pulled something, not doing great right now," Bednar said. "He'll get reevaluated tomorrow." … San Jose went 3-2-1 in six games without Boughner, with assistant John MacLean filling in as coach.
Sharks forwards Kevin Labanc and Matt Nieto, and defensemen Erik Karlsson, Jake Middleton, Radim Simek and Marc-Edouard Vlasic also played after being removed from NHL COVID-19 protocol. … Avalanche forward Gabriel Landeskog has eight points (three goals, five assists) in his past five games. … Burakovsky has four points (three goals, one assist) during a three-game streak.