Steen scored two goals, including the tiebreaker 4:32 into the third period, and had an assist in a 6-3 Blues victory at Scottrade Center. He missed the previous two games with a lower-body injury.
"We've been put together maybe one or two games this year and seemed to break up in the middle of the game, but tonight we found that chemistry that we left off with last year," said Oshie, who had a goal and two assists. "All three guys were working, and when we're doing that, that's when we get all our success."
The Blues weren't sure Wednesday whether they'd have Steen, Backes (facial lacerations) or Jay Bouwmeester (groin) for the game, but they helped the Blues' cause.
Steen has 18 points (five goals, 13 assists) in 17 games against the Islanders.
"I thought all the guys that came back in gave us some structure and some continuity in our lineup," Blues coach Ken Hitchcock said. "... I thought [Steen] was real good; I thought that line was real good. They set the tempo early in the hockey game, set the tempo in the third period. That's what we need.
"To me, the points are coming because of it. Points aren't coming because they're just playing hockey. They're playing hockey the right way and it's a big line that can compete. They're getting it everywhere. They're looking more and more like they did last year to be honest with you, which is real good for us."
With the game tied 2-2, Backes threw a puck high off the glass in his zone, Oshie won it at center ice to create a rush into the Islanders zone, fired a shot at former Blues goalie Jaroslav Halak, and Steen knocked in the rebound.
"I was shooting for a rebound there," Oshie said. "I tried high blocker once and then I don't know if I tried five-hole on [Halak] already, but I figured I'd shoot for a rebound. I saw guys coming from the weak side. Luckily, [Steen] was there."
Oshie took Patrik Berglund's behind-the-net pass in the slot and beat Halak high glove side with 4:13 remaining to make it 4-2.
Stastny has a four-game point streak (four goals, one assist).
The victory was the Blues' third in a row and their second against the Islanders in six days. St. Louis has defeated the Islanders five straight times and seven of the past eight.
Halak, playing his first game in St. Louis since being traded by the Blues last season, made 27 saves. He faced the Blues for the first time Saturday in a 6-4 loss.
It was New York's third consecutive loss, their second such streak this season, and the Islanders have given up 17 goals in the most recent.
"Right now we're trying to dig ourselves out for a win," Islanders center Brock Nelson said. "There's a little bit of adversity but at the same time that's what makes you a better team and you've got to learn from what we need to build off and continue to focus on what we need to do. If you keep continuing to work hard, the results are going to come."
Islanders coach Jack Capuano has put his players on notice if the bad trends continue.
"We'll give up five a night if we keep mismanaging the puck," Capuano said. "They'll figure it out sooner or later, and if not, they won't be in the lineup."
Tavares scored with 3:57 remaining in the second period after the Islanders won an offensive-zone faceoff and his shot dribbled through Allen's legs.
Late in the period, Frans Nielsen poked a faceoff win forward, and Grabovski caught the Blues and Allen napping with a wrist shot from the high slot with 5.3 seconds remaining.
"We just let our foot off the gas for three minutes," said Allen, who is 9-3-1. "A team like that that's so offensive, they took advantage of the opportunities.
"It's tough letting a goal in with five seconds of a period. But the guys came out strong in the third, which to me, is pretty impressive to watch that."
With Islanders defenseman Brian Strait off for interference, the Blues were able to get good movement on their first power play of the game. Steen stepped into a slap shot from straight away that beat Halak 5:58 into the first period.
Jackman made it 2-0 at 14:18 of the first when Steen found the defenseman with a cross-ice pass and Jackman stepped into a slap shot from the top of the left circle that went in off the right post.
It was Jackman's first multipoint game since March 13, 2013, against the San Jose Sharks.
Bouwmeester missed eight games and played 20:59 in his first game since Nov. 22.
"There's a lot of elements to like," Hitchcock said. "This is the likes and dislikes of our season. Tonight's game is a microcosm of our season. We've got great spirit, which is stuff you love, but understanding and managing the game the right way, I think it's going to be important that we figure out when the other team's got the push, then that's when we've got to have the right push back."