Jonathan Quick made 21 saves and Drew Doughty scored his first goal of the post-season for the defending Stanley Cup champions, who won four straight to finish off fourth-seeded St. Louis.
Penner put the Kings ahead with his latest big playoff goal, ripping a slap shot from just inside the blue line past Brian Elliott right before time expired.
Elliott stopped 14 shots and Chris Porter scored his first career playoff goal for the Blues, who were eliminated by Los Angeles for the second straight season, this time despite taking a 2-0 series lead.
Maple Leafs 2, Bruins 1
BOSTON (AP) — Tyler Bozak and Clarke MacArthur scored and James Reimer stopped 43 shots to help Toronto stay alive in the first-round playoff series.
Game 6 is Sunday in Toronto, with the decisive seventh game back in Boston on Monday, if necessary.
Boston has won both games in Toronto in the series and has not lost on the Leafs' home ice in the playoffs since 1959.
Zdeno Chara scored for Boston to cut the deficit to it 2-1 with 8:48 left. The Leafs killed off a delay-of-game penalty in the last four minutes and then protected the lead when the Bruins pulled Tuukka Rask for an extra attacker with 1:11 left.
Rask made 31 saves.
Only once in their history have the Leafs come back to win a playoff series after falling behind 3-1: In the 1942 Stanley Cup finals, when Toronto won four straight to take the title after losing the first three games against Detroit. The Bruins are 15-2 in playoff series after taking a 3-1 lead, but they blew a 3-0 lead against Philadelphia in the 2010 Eastern Conference semifinals.
Capitals 2, Rangers 1, OT
WASHINGTON (AP) — Mike Ribeiro scored 9:24 into overtime, and the Capitals regained the momentum — and the lead — in their first-round playoff series.
Ribeiro put in the puck after Troy Brouwer deflected a shot from the blue line.
The Capitals lead the series 3-2. Game 6 is Sunday in New York.
The home team has won every game in the series, with Washington taking the first two and New York pulling even in Games 3 and 4. The Capitals have been fighting history along the way: The franchise has lost eight playoff series in which it has held a two-game lead.
Brian Boyle scored for New York in the first minute, but that was it for New York's offence. Joel Ward tied it in the second period.
DETROIT (AP) — Henrik Zetterberg scored his second goal 1:04 into overtime, forcing a Game 7.
Detroit blew a two-goal lead in the last 3 1/2 minutes of the third period, sending the team to a fourth OT in a series for the first time in franchise history.
Emerson Etem and Bobby Ryan scored 51 seconds apart late in regulation to pull the Ducks into a 3-3 tie.
Zetterberg, who scored a go-ahead goal 6:19 into the third period, had a shot to win it with about a minute left. But his shot hit the right post and slid across the crease.
Second-seeded Anaheim will host seventh-seeded Detroit on Sunday night in the deciding game.