Andersson and MacKenzie Weegar each had a goal and two assists, and Elias Lindholm had a goal and an assist for the Flames (31-24-15), who have points in four straight (2-0-2). Markstrom made 20 saves.
Calgary trails the Winnipeg Jets by four points for the second wild card into the Stanley Cup Playoffs from the West.
"We've got to just win," Weegar said. "We've got to find a way to win. And win every game going forward.
"We're big boys in here. We do a good job keeping the positivity and keeping the confidence high. What are we going to do? Dwell on it and let it crush us? No. We've got 12 games and we've got to win. We've got to keep going here."
Andersson gave Calgary a 5-4 lead at 9:53 of the third period when he beat a stickless Oettinger through a screen from the right point.
Jani Hakanpaa
tied it 5-5 at 12:09 when his wrist shot from the right hash marks bounced in.
"I think there were a lot of swing of emotions," Robertson said. "There were 11 goals. I mean, it's kind of funny. I don't know who I was talking to in the intermission but I was like, 'This isn't like playoffs last year (in the Western Conference First Round), right?' Every game was 1-0, 2-0. This season, every time we play them, it's 6-5, 5-4, 6-5. It is what it is, but I'm glad we got the better end tonight."