The win was the second straight for the Blues after losing 11 in a row. St. Louis won back-to-back games in regulation for the first time this season, and improved to 1-6-1 at home.
The victory snapped the Kings' five-game winning streak against the Blues. The last St. Louis win over Los Angeles since March 16, 2004.
Backes' first NHL goal came on a backhand in the slot at 10:47. Backes, a second-round pick in 2003 who is staying with veteran Keith Tkachuk, made his debut Tuesday in Pittsburgh and had an assist.
"Keith went hard to the net and took two guys with him and left a ton of room in the slot for me," Backes said. "(Radek) Dvorak passed it out there and I just threw it on and luckily it found the back of the net."
Backes credited his teammates with helping him adjust to life in the NHL.
"The guys are making it easy for me, simplifying my role," Backes said.
Tkachuk said the rookie has what it takes to succeed in the league.
"He got our team going," Tkachuk said. "He's a big, strong kid. With the new NHL rules, it's power, power, power. Once he gets a step on a guy with his speed and size, he's going to create a lot of things. You can tell he's got a good nose for the net."
"That ability will serve him well," St. Louis coach Andy Murray agreed.
"He won the puck battle down in the corner and powered his way to the net," Murray said. "It was a power forward goal."
The Blues took a 2-0 lead at 6:10 of the second period when Stempniak scored on a wrist shot from the top of the left circle. Stempniak's shot went over the glove of Kings goalie Dan Cloutier and into the upper right corner of the net.
"They tried to sneak in a line change and (Barret) Jackman turned it up quick and I got off a shot before they could cut me off," Stempniak said.
St. Louis went ahead 3-0 at 11:01 when Martin Rucinsky scored on a rebound in front of the net. Dennis Wideman ripped a slap shot from inside the blue line that Cloutier blocked. Battling two defensemen, Rucinsky knocked in the loose puck.
The Kings struck twice quickly early in the third period to get back in the game.
Anze Kopitar used his backhand to score at 1:40. In his last five games, the 19-year-old center has five goals and three assists.
"I feel great. I feel confident and comfortable," Kopitar said. "My teammates and my coach have a lot of confidence in me."
"In the third period, we got back to doing the basic things that made us successful," Los Angeles coach Marc Crawford said.
After the Kings outshot the Blues 10-0 in the first 10 minutes, St. Louis regained some momentum. Jamal Mayers found a Jay McClement streaking toward the net and put the puck on his stick. McClement rammed the home the goal at 9:37 for a 4-2 lead.
"We were not sharp at the start of the third period but we woke up and got a big goal by McClement's line and won the game," Tkachuk said. "It's a great feeling."
Jackman added an empty-net goal with 21 seconds left. It was his first goal of the season.
- Murray's last win as Kings coach before he was fired was a 3-1 decision against the Blues on March 18. "I've got a lot of friends over there. They're my second favorite team in the Western Conference," Murray said.
- the Blues have scored the first goal in all six games under Murray
- The Blues have allowed a power-play goal in their last nine games. St. Louis has been short-handed 39 times in Murray's six games.
- The Blues assigned forward Trent Whitfield to the Peoria Rivermen, the club's AHL affiliate.