Last November the Galaxy capped perhaps the most dominant season in Major League Soccer history by beating the Houston Dynamo to win the MLS Cup.

On Tuesday it continued one of the steepest declines in league history, losing to a previously winless second-tier team in the Lamar Hunt U.S. Open Cup.

It’s been a precipitous and humbling fall for a star-studded Galaxy team with a Hall of Fame coach that pays its top three players more than 17 other MLS teams spend on their entire payrolls. It’s as if the New York Yankees suddenly started losing to junior college teams.

While the analogies come easily, however, valid explanations for how the Galaxy went from dynasty to demise do not. The decline has been blamed — at various times and with differing levels of intensity — on the absence of injured defender Omar Gonzalez, on fatigue, on a lack of effort and on a changing chemistry in the locker room.

In a way, though, it’s been a perfect storm of disaster, with the Galaxy losing players to rehab, injury, suspension and international duty. David Beckham even missed a start after flying back to Europe to participate in the Olympic torch relay.

“Internally, we know the issues,” Coach Bruce Arena said Thursday. “And I’m confident we’re going to break out of this.

“We’ve got to get a few breaks and we’ll turn this thing around.”

The biggest loss, however, might simply be a loss of interest. Landon Donovan came close to admitting as much 10 days ago when he sat down with reporters at the U.S. national team training camp.

“I think all players reach a point in their career where it’s natural to lose some of that hunger, that desire, to sort of break out or be a star,” he said. “My mind-set now is I want to be successful, and I realize now that as I’m getting older I’m not going to be the guy who’s scoring goals every game or making a great impact all the time.”

And that was the Galaxy captain speaking.

The stats, though, bear him out. Donovan, who has missed the Galaxy’s last two matches because of international duty, started 10 of the team’s first 11 games, registering two goals and two assists. Through his first 10 Galaxy starts last season he had scored eight times.

Last season the Galaxy lost just once in Donovan’s first 10 starts. This year they’ve lost half the time.

But though Donovan may be the only one willing to speak up candidly he is hardly the only one worthy of blame. The team’s other two superstars — forward Robbie Keane and midfielder Beckham — have been ineffective for wide swaths of the season.

Keane, who is with the Irish national team for Euro 2012, hasn’t scored in two months. And after taking nine shots on goal in his first three games he’s had just five since. Beckham, meanwhile, has already matched his goal output from last season and has almost as many assists after 10 starts. But at times he’s also looked very much like what he is — a leg-weary 37-year-old in the fading twilight of his career.

How dire is the Galaxy’s situation? More than a third of the way into the season the team is not only last in the conference standings, but it’s tied for last in the West in wins (three), has the second-most losses in the league (eight) and trails just one other MLS team in goals allowed (21).

Last year the Galaxy didn’t allow its 21st goal until September.

To reach the postseason, the Galaxy needs to finish in the top five in its conference, and last year that took a minimum of 49 points. This year’s Galaxy needs 38 points over its final 21 games to match that.

Simply mentioning that sounds like concession to Arena.

“You can put your math somewhere else right now,” he said. “It’s a little early for that. But the easiest way to take care of yourself is to win games. If we don’t win games we’re not going to make the playoffs.”

The Galaxy will have Donovan back for its next game June 17 and Keane should be back shortly after that. And though the team hasn’t said so officially, Gonzalez, the league’s defender of the year in 2011, is recovering from off-season knee surgery faster than expected and he, too, could be on the field by July.

But winning will require more than showing up. It requires some backbone too. And Arena appears ready to supply that.

When the U.S. team was upset in the Olympic qualifier earlier this spring, Arena, a former national team coach, was asked what the repercussions might be. “Usually the scapegoat for every competition is the coach,” he said.

Asked Thursday whether the same standards apply with the Galaxy, Arena didn’t flinch.

“I’m a big boy. I don’t run away from that stuff,” he said. “It’s a little of everything. It’s not just coaching. It’s not just players. It’s both. A lot of things that could be better aren’t better. That’s the responsibility of our organization.

“But every team faces that. You can’t use that as an excuse.”

kevin.baxter@latimes.com