Whether it was the emotional victory over the defending Stanley Cup champions or the fact it was playing for the sixth time in 10 nights, the Wild’s fuel tank was on empty for the first 40 minutes Monday night.

No legs. No energy. And no cohesion against a desperate St. Louis Blues team that, perhaps buoyed by an in-game trade for Calgary thoroughbred defenseman Jay Bouwmeester, took advantage of the Wild’s lethargy and poor execution to move back into the top eight in the Western Conference with a 4-1 victory.

“We were flat. We got what we deserved. We didn’t play well at all,” Zach Parise said. “It was pretty similar to the team that we started the season. That’s the type of game we played — not competitive, and too many turnovers.

“It’s crept back into our game. The last few games we’ve gotten away with it. Tonight, against a team like that, you’re not going to.”

Despite the Wild having won eight of its previous nine games, many in the restless Xcel Energy Center crowd booed the Wild off the ice after the second period and at the game’s conclusion.

“It levels us back down to Earth a little bit,” Devin Setoguchi of the loss.

The Wild was beaten to loose pucks all night, lost battles all over the ice and looked slow.

“We got outbattled. We weren’t ready for a physical game and it showed,” said center Kyle Brodziak.

It was a tough loss for the Wild, which now heads on a three-game road trip to San Jose, Los Angeles and Columbus. The Wild lost a significant player to injury, too. Veteran center Matt Cullen, who makes the second line go and is the team’s fourth-leading scorer, didn’t play the third period.

Coach Mike Yeo said he will have an update on Cullen’s injury Tuesday. If serious, it will be interesting to see if General Manager Chuck Fletcher reacts with the trade deadline at 2 p.m. Wednesday. The Wild isn’t carrying any extra forwards, so a call-up from Houston is likely if Cullen is sidelined.

The thing that annoyed the fans off the most was the Wild’s ineptitude on a third consecutive power play in the second period. After the Wild pulled even on Dany Heatley’s goal the instant a power play expired early in the period, the Wild had all the momentum. It even forced St. Louis into three icings on one shift soon after the goal.

But the Wild drew another power play, and it was a momentum killer. The Wild didn’t come close to scoring against Brian Elliott, who replaced an injured Jaroslav Halak in the St. Louis net late in the first period.

The Blues responded with back-to-back goals by Andy McDonald and Kevin Shattenkirk 1:50 apart. Down 3-1, the Wild drew two more power plays and both were abysmal. The last power play, Pierre-Marc Bouchard’s center-ice turnover ruined nearly a minute.

Setoguchi said the Wild cheated and “took shortcuts.”

“They pushed the pace to us, and we just sat back and had to react. We weren’t the aggressors,” Setoguchi said.

The Wild also showed its frustration in the first. For the third consecutive game, referees missed a Wild player being high-sticked. This time it was captain Mikko Koivu, who missed 10 minutes because of a cut to the left of his nose. Ryan Suter yapped enough to soon be called for unsportsmanlike conduct.

After Suter got out of the box, Tom Gilbert couldn’t clear the puck thanks to referee Ian Walsh being in his path. Gilbert was then tripped by Patrik Berglund. There was no call, and a Suter turnover later, Jaden Schwartz scored.

Regardless, Yeo and players said the defeat was a “wake-up call.”

“We got a good reminder that both defensively and offensively, things are not going to go your way if you play that way,” Yeo said.