The Kings' defenseman scored his 25th career goal at an opportune time in his 664th NHL game.
Mitchell snapped a third-period tie with his first goal of the season with 5:49 left in the game to help the Kings to a 3-2 victory over the St. Louis Blues on Tuesday night.
"It was big and his first of the season and I think he's been waiting for that one for a while," Kings captain Dustin Brown said of Mitchell. "It's really nice to get it at this time."
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Mike Richards scored a goal and assisted on another, the Kings got a team-leading 10th goal from Anze Kopitar, and Jonathan Bernier stopped 23 shots in only his fourth start of the season as the Kings won in St. Louis for just the third time in 11 tries.
"It was a difficult game," Kings coach Terry Murray said. "St. Louis came out in the first period and they were putting on a lot of pressure on the puck over top of us. It ended up being a pretty exciting hockey game."
Alex Steen and Vladimir Sobotka scored for the Blues, who lost for only the second time in regulation in 10 home games. Jaroslav Halak stopped 25 shots.
"I think the last two games in the last two periods, we've probably come off it a little bit in the third period," Blues coach Ken Hitchcock said. "We've kind of been the team making a few mistakes. We've made a couple errors in our own end that have ended up in our net or ended up us taking a penalty to give the momentum back to the (opposing) team.
"It's a frustrating loss for the players to battle back like we did and give it up so quickly. It's a tough loss."
The Blues were not pleased with a play at the end of the game in which Kings defenseman Drew Doughty took St. Louis' T.J. Oshie hard into the corner boards. Oshie skated off with a trainer holding his left shoulder and head, but Doughty was assessed only a two-minute cross-checking penalty.
"The end result is a two-minute penalty and a face-off outside the zone," Blues captain David Backes said. "They might as well just run clock on that.
"I guess if that's the extent of it, that's a good way to kill the clock ... no holds barred at the end of the game. But it can't come down to the last 3 seconds. We should have been in better position, where it's us closing out that game."
Mitchell's shot from the left point got through after the Blues' Scott Nichol went down to block the shot but it beat Halak on the near side with 5:49 remaining.
Steen put the Blues up 1-0 with his team-leading eighth goal of the season just 1:07 into the game off a nice give-and-go play with Oshie.
The Kings' Kopitar scored the tying goal 7:36 into the second, a power-play goal after Richards picked off Barret Jackman's turnover in the right corner, feeding Kopitar in the crease, beating Halak.
Patrik Berglund nearly gave the Blues the lead twice late in the second period, once after stripping a puck at the blue line short-handed and creating a 2-on-1 breakaway. But Berglund couldn't finish his shot as Bernier made a shoulder stop. Berglund also had Bernier rob him in the slot on a backhand after taking Sobotka's feed.
"The difference for us was when we had all the chances in the second period and we couldn't grab the lead," Hitchcock said. "For me, that was disappointing."
Richards broke a 1-all tie in the third when Andrei Loktionov picked off another Jackman puck, fed Richards in the slot and he beat Halak cleanly 4:41 into the period.
"It's nice to help the team have success," said Richards, acquired over the summer from Philadelphia. "I think I struggled earlier (in the season).
"I think trying to get adjusted to the new team and sometimes I think you try to make too many plays when things like that happen. But I'm just trying to get the puck in the net as much as possible and starting to feel a little more comfortable with linemates and just getting pucks to the net as much as possible is the biggest thing."
Jackman, who's been solid for the Blues this season, said the turnovers are no excuse.
"The first one on the (penalty kill), I just made a bad read with good players on the ice," Jackman said. "I thought the play was in the middle, but obviously it wasn't and they jumped on it and scored.
"The second one, the puck just bounced over my stick. It was going the wrong way and I couldn't recover."
Sobotka got the equalizer for the Blues, finishing off Matt D'Agostini's pass in the left circle with 7:32 remaining.
"That last power play was very, very effective," Hitchcock said. "I think it gave us momentum leading up to (Sobotka's) goal. But when you're scoring two goals a game, you're living on a fine line. We've been on the right side of it for the most part. But we're going to have to extend ourselves a little bit better if we expect to win."
Murray (61) and Hitchcock (59) are the oldest coaches in the league. They have a combined 2,052 games coached between them; Hitchcock with 1,048, Murray 1,004. ... The Blues' top line of David Backes, Oshie and Steen has 13 points in five games. Oshie has nine points in nine games. ... Richards has now scored five goals in four straight games and has eight points in six games. ... Bernier made only his fourth start. ... The Blues placed D Carlo Colaiacovo (hamstring) on the injured list retroactive to Friday.
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Arena: Scottrade Center Location: Saint Louis, Missouri
Referees: Frederick L'Ecuyer, Chris Rooney Linesmen: Mark Wheler, Matt MacPherson
Attendance: 18,178 (94.9% full)
Team Stat Comparison
Power Play Goals
Power Play Opportunities
Shots on Goal
Alexander Steen (8)
Assist: T.J. Oshie
Anze Kopitar (10)
(Power Play) Assist: Mike Richards
Mike Richards (9)
Assist: Andrei Loktionov
Vladimir Sobotka (2)
Assists: Matt D'Agostini, Kris Russell
Willie Mitchell (1)
Assists: Simon Gagne, Justin Williams