ST. LOUIS -- Derek Roy needed less than 2 minutes to redeem himself Thursday night.
St. Louis won for the sixth time in eight games. The Islanders have lost eight straight overall (0-6-2) and eight in a row on the road.
David Backes, Jay Bouwmeester, Magnus Paajarvi and Brenden Morrow also scored for the Blues, who improved to 12-1-2 at home and tied Boston (12-3-2) for the most home victories in the NHL. Jaroslav Halak made 22 saves and upped his record to 15-4-2.
Andrew MacDonald scored for the Islanders, who are 2-11-2 in their past 15 games.
Roy took a tripping penalty that led to MacDonald's tying power-play goal at 5:19 of the second period.
"I was pretty mad about the penalty," Roy said. "And they ended up scoring on it. When I got out of the box, I wanted to redeem myself -- and luckily I got the chance to."
Roy pounced on the rebound of a shot from Kevin Shattenkirk to give the Blues a 2-1 lead at 7:02.
"I think he felt better about himself," St. Louis coach Ken Hitchcock said of Roy. "His goal seemed to energize us."
Just more than 2 minutes later, Backes scored a power-play goal on a wrist shot from the top of the circle. Paajarvi increased the advantage to 4-1 with his second of the season, capping a three-goal burst in 7:57.
"It was a huge period for us," Paajarvi said. "The whole team really came back to its game."
St. Louis was 3 for 6 on the power play after managing one goal in its previous 10 chances.
"The power-play goals really put us in a hole," New York center John Tavares said. "It's the same thing again. [We're] just not good enough."
St. Louis' power play struggled in back-to-back losses to San Jose and Los Angeles, the team's first two-game regulation losing skid of the season. Shattenkirk, who assisted on two man-advantage goals Thursday, said the club made it a point to shore up the unit.
"We just got back to simple things, getting pucks to the net and working on winning the battles," he said. "We got back to what we do best: shooting pucks and getting bodies out in front."
New York goalie Anders Nilsson lost for the first time in regulation in his third start of the season. He made 21 saves.
"We all know in the locker room that we have to step it up," Nilsson said. "Everybody has got to look in the mirror and see what you can do better."
The Islanders, who are 3-10-0 on the road, have given up a league-high 27 power-play goals.
"It's tough what we're going through," Tavares said. "The only thing that is going to get us out of it is better execution."
The Blues are 11-0-1 when leading after the first period. ... Islanders G Evgeni Nabokov, who is out with a groin injury, practiced Wednesday and could rejoin the team in a week. ... New York started a five-game road swing that will end Dec. 12 in Phoenix. ... Paajarvi was back in the lineup after missing the previous game with the flu. ... St. Louis won the previous meeting between the teams 5-1 on Feb. 16, 2012. ... The Blues killed off 15 successive penalties at home before MacDonald's power-play goal in the second period.