ST. LOUIS — The Rangers arrived at Enterprise Center on Saturday feeling good about their play over the past week.

The reigning Stanley Cup champs quickly put an end to that.

The Rangers had a few costly mistakes that led to quality chances and the Blues pounced, running away with a 5-2 victory Saturday night.

Coach David Quinn had called facing a team like the Blues (29-10-7) a “benchmark game,” especially after the Rangers came in encouraged by back-to-back wins and a strong performance in a loss to the Canucks before that. But the Rangers (21-19-4) failed to back up those efforts.

“It’s frustrating. We can’t get anything going,” Mika Zibanejad said. “We get max two wins in a row and then we get back to losing. Obviously it’s frustrating. It’s simply not good enough.”

The Rangers have won three straight games just once all season, missing another chance to do so Saturday night.

Getting his first action in nine days, Henrik Lundqvist made 24 saves, but did not get much help in front of him. He faced just 29 shots — compared to some of the high-volume onslaughts the Rangers have allowed this season — but got hung out to dry on multiple occasions.

“A couple chances there where we make mistakes,” Lundqvist said. “At the end of the day, as a goalie, you need to come up with a save there to make a difference.”

FIlip Chytil had a strong effort with a goal, which gave the Rangers a 1-0 lead in the first period, and an assist.

They had a chance to build on it with a four-minute power play a few minutes later, but instead let it backfire. The Blues gave them nothing and killed it off before quickly tying the game. Robert Bortuzzo jumped out of the box and took a pass from Ivan Barbashev for a breakaway and scored to make it 1-1, just six seconds after the penalty expired.

“I really thought that four-minute power play really put us back a bit,” Quinn said. “They seemed to get energy off of that, we got a little bit demoralized.”

Vince Dunn gave the Blues the 2-1 lead with 1:19 left in the first period on a clear shot from the left circle. Lundqvist got a piece of his glove on the puck, but not enough of it.

Pavel Buchnevich took an early second-period hooking penalty and it quickly came back to hurt the Rangers. David Perron was left open in the left circle for a one-timer and ripped it past Lundqvist to make it 3-1 at 1:26.

Chytil set up Brett Howden for a goal that made it 3-2 midway through the period, but the Blues answered less than two minutes later, slamming the door shut. Zach Sanford beat Libor Hajek for a puck in the neutral zone and opened up a two-on-one with Barbashev against Tony DeAngelo. Sanford finished off a one-timer for the 4-2 lead.

“We were doing some good things,” Quinn said. “We make a bad mistake in the neutral zone and give up a two-on-one. We had people in the right place, it was just some big individual mistakes that cost you where they [the Blues] don’t seem to make those. We made them in a dangerous area.”

Jaden Schwartz made it 5-2 before the second period was over after deflecting a pass on another Blues rush, the kind the Rangers gave up too many of and didn’t get enough of for themselves.

“That’s frustrating,” defenseman Brady Skjei said. “Getting off to a 1-0 start and we kind of — not fall apart, but definitely stop managing the puck like we used to, like we had done in the past. It just got away from us.”

For more on the Rangers, listen to the latest episode of the “Up In The Blue Seats” podcast: