ST. LOUIS -- Alexander Steen's contribution to the St. Louis Blues in the playoffs could not be accurately measured in the box score -- until Tuesday night.

Steen, who often draws the assignment of defending the opponent's top line, scored two goals, as did David Backes, to lead the Blues to a 6-1 win over the Dallas Stars in Game 3 of a Western Conference semifinal series.

The Blues scored six unanswered goals after the Stars took a 1-0 lead, and they now lead the best-of-seven series two games to one.

"It's nice to chip in," said Steen, who scored only one goal in the Blues' first nine playoff games. "We've had that mentality as a group, we have our roles going into the playoffs, and the number one thing is getting wins."

Steen's first goal came 57 seconds after Colton Sceviour gave Dallas the lead just 4:44 into the game.

A power-play goal by Backes at 16:10 put the Blues in front, but the Stars thought they tied the game with 1:19 to play in the period. A video review overturned the would-be goal by Jason Demers, which hit the crossbar and never went in the net.

"The game changed on the non-goal," Blues coach Ken Hitchcock said. "Emotionally, we could have gone in tied, and we ended up going in up, and that was a big swing in the momentum of the game. Instead of being discouraged, I thought we were really in a different mental frame. Inches or whatever, but that crossbar gave us a different attitude coming out for the second period."

Different indeed. The Blues were outscored 12-3 in the second period in their nine previous playoff games, but in this game, they pounded the Stars with 16 shots on goal and scored three times in the second. Troy Brouwer, Vladimir Tarasenko and Steen collected the goals, turning a 2-1 game into a 5-1 rout.

Backes completed the scoring with his second goal, a short-handed tally with 1:54 to play in the third period.

Tarasenko added two assists to his goal. He has five goals in this year's playoffs, 15 in 22 career postseason games.

Steen has not had that kind of production offensively, yet he remains a key to the Blues' success.

"He's our best player," Hitchcock said. "Alex is our best player. I want him playing against the top players. He loves that challenge, he loves that focus. He just rises to the occasion. He does a lot of things underrated, but the coaches notice the little things. He's one of the most complete players in the league."

Brouwer's goal chased Stars starting goalie Antii Niemi, but Kari Lehtonen didn't fare any better. Just 1:16 after Lehtonen entered, he gave up the goal by Tarasenko that deflected off the skate of Dallas defenseman Alex Goligoski.

It was the second game in a row in which the Stars pulled their starting goalie, with Niemi coming off the bench to replace Lehtonen in Game 2. Even so, Goligoski said nobody was blaming the goalies for the two losses.

"We're giving up some big chances at bad times; it hasn't been a goalie issue," Goligoski said. "Losing confidence in our goalies is not an issue. Things can change quickly. It's a game we've just got to flush away. It's a game maybe where there were not any bright spots for us."

One of the negatives was going 0-for-4 on the power play, leaving the Stars 0-for-11 with a man advantage in the series. Two of the Blues' goals came on the power play, giving them four goals in 14 opportunities.

"It's never good when you lose like that in the playoffs, but the good thing about that is this is a seven-game series," Stars left winger Jamie Benn said. "In the playoffs, you've got to have a short memory, so we're going to move on and get ready for the next one."

NOTES: LW Curtis McKenzie made his Stanley Cup playoff debut, inserted into the Stars' lineup on the fourth line. He only played in three games in the regular season but took the place of RW Valeri Nichushkin. ... The Stars were without C Tyler Seguin (Achilles) and RW Patrick Eaves (leg), although coach Lindy Ruff said Eaves possibly could return for Game 4 on Thursday. Nichuskin had replaced Eaves in Game 2. ... The Blues kept RW Ryan Reaves in the lineup and scratched RW Steve Ott for the second consecutive game. ... After Game 4 on Thursday night in St. Louis, the series will return to Dallas for Game 5 on Saturday.