Steen broke down the left side as part of a 3-on-1 rush. He kept the puck and let go a drive from just inside the circle that trickled through Crawford.
The Blues (3-0) matched their best start to a season, also done in the 1969-70 and 1993-94 campaigns. Jaroslav Halak made 26 saves in his third straight win. Vladimir Tarasenko and David Backes also scored for St. Louis.
KINGS 4, SENATORS 3, OT
Dustin Brown scored twice during the Kings' three-goal first period, and Carter had three points in Los Angeles' sixth straight home victory over Ottawa in the past decade.
Milan Michalek scored the tying goal with 4:27 left in regulation for the Senators. Jean-Gabriel Pageau netted his third career goal in the second period, and Bobby Ryan scored his first goal with Ottawa early in the third.
Craig Anderson stopped 28 shots as the Senators opened a four-game Western road swing that is part of their season-opening six-game trip. He has one win in 11 career decisions against Los Angeles.
FLAMES 3, CANADIENS 2
MacDonald made his third consecutive start.
P.K. Subban had a goal and an assist for the Canadiens (1-2), who hadn't played since beating Philadelphia on Saturday. Lars Ellar recorded his fourth goal and sixth point of the season. Carey Price made 22 saves.
Despite being outshot 12-4 in the first period, the Flames took a 2-0 lead.