Barbashev, Steen and Sundqvist have 14 points (six goals, eight assists) in 17 playoff games. Sundqvist, the center, has six points (three goals, three assists), right wing Steen has four points (two goals, two assists), and left wing Barbashev has four points (goal, three assists).
"They've been really good in all facets of the game," Blues coach Craig Berube said. "[We're] not only getting some secondary scoring from them, but just put them against any line out there and they do the job. Penalty killing, checking, just all the little things."
On the first shift, against the productive San Jose line of Gustav Nyquist, Logan Couture and Timo Meier, Steen pressured Sharks defenseman Brent Burns behind the net. Burns' pass went right to Barbashev, whose shot deflected off Nyquist's stick past goalie Martin Jones for a 1-0 lead.
"Just look at that start they had, it kind of set the tone for the night," Blues forward Ryan O'Reilly said. "But they're a line, you put them in any situation and they're effective. They got our team going with a huge goal, huge first shift. They gave that team trouble all night, and that just shows the depth of our team, how strong we are."
Blues forward David Perron said he doesn't consider them a fourth line.
"They're playing really good hockey, around 15 minutes a night, and that's what we need from those guys," Perron said. "They play solid, they can play against any line. They bring momentum to our club shift after shift."
Steen played 15:14, Sundqvist played 15:10 and Barbashev played 12:49 in Game 4. They had three shots on goal, four hits, and helped kill three of four Sharks power plays.
"Every time we play physical, and every time we have a chance to get some [offensive] zone time, it's momentum. I feel like it's momentum for everyone, every other line," Barbashev said. "From the start of the series, we're working so hard. I just think the last couple games we're getting rewarded."
NHL.com correspondent Louie Korac contributed to this report