OAKLAND, Calif. — The Golden State Warriors have four all-stars, all of whom are comfortably among the top 20 players in the NBA. That talent advantage has allowed them to cruise through the past two seasons virtually unchallenged, leading to an NBA championship last season and making them overwhelming favorites to win one again this year.

But even as the Warriors have remained in position to win a second straight title, they have built a roster with vulnerabilities that could derail their run.

And suddenly, after a 95-92 loss to the Houston Rockets on Tuesday night in Game 4 of the Western Conference finals at Oracle Arena, what was supposed to be a relatively easy march to a second straight NBA crown has been met with stiff resistance.

“It’s all about toughness right now,” Rockets Coach Mike D’Antoni said after his team showed that trait in spades to even the series. “I think there was great basketball played on both sides, stretches of it.

“The rest of it is just gutting it out and finding a will, a way and a want.”

Golden State has rarely needed to find any of those things over the past two seasons. Last year, the Warriors won 15 straight playoff games before losing Game 4 of the NBA Finals to the Cleveland Cavaliers. They then promptly won Game 5 and won the title.

The Warriors brought back 12 of the 15 players from last year’s title team — including their four all-stars and key bench pieces in Andre Iguodala, Shaun Livingston and David West (all of whom re-signed last summer) — and still have one of the league’s elite coaches in Steve Kerr.

So what could go wrong?

The Warriors have such a talented top-end of their roster — those four all-stars (Stephen Curry, Kevin Durant, Klay Thompson and Draymond Green) allow the Warriors to always have at least two of the top 20 players in the league on the court at once, while no other team in the NBA even has more than two of them, period — that the strange nature of the rest of the roster was glossed over for much of the season.

But the two main free agent additions Golden State made last summer — signing Nick Young for the taxpayer’s mid-level exception and Omri Casspi to a minimum deal — were spectacular failures. And carrying six centers, making up a staggering 40 percent of the roster, in a league that has trended toward playing smaller and faster for years (in no small part because of the Warriors’ own success), never made any sense.

Those decisions left the Warriors vulnerable to precisely the position they found themselves in Tuesday night. With no Iguodala, who missed the game with a lateral contusion in his left leg, and no Patrick McCaw, who has been out since suffering a spine contusion March 31 after a rough fall against Sacramento, the Warriors essentially were left with an eight-man rotation for their biggest game of the playoffs.

One of those players was Young, who was a putrid minus-14 in 12:30 while scoring two points — an exclamation point on what has been a staggeringly bad one-year deal.

Young was supposed to provide scoring on the second unit and depth on the wings. Instead he flitted in and out of the rotation all season, splitting a spot with McCaw before McCaw’s injury. Given Golden State was the heavy favorite to win a title, that $5.2 million contract should have brought them significant value from a role player who wanted to win. Young has provided virtually none.

Casspi, on the other hand, isn’t even on the postseason roster. His season was completely derailed by injuries, and he was eventually waived before the playoffs so Golden State could convert former DeMatha High star Quinn Cook’s two-way contract into a minimum deal.

A switchable forward defensively capable of stretching the floor from three, Casspi would have been exactly the kind of player the Warriors could use in a matchup against the Rockets. Instead, they have Cook, who played two minutes in the second quarter of Game 4 because of foul trouble for Curry and only appeared in garbage time in Games 2 and 3.

It’s not that cutting Casspi was a mistake — Cook helped Golden State when Curry was injured, and he deserved the spot. But what Casspi was supposed to be for the Warriors would be awfully useful right now.

Instead, the Warriors find themselves in a dogfight with a more than game Rockets team, and they have a roster that lacks the right depth to face it.

This was precisely the moment Houston has spent the past year building toward, and the Rockets have been incredibly impressive in this series. Still, even the Rockets would have admitted they needed some breaks — and they have gotten them.

Curry’s conditioning is still a work in progress after he missed seven weeks with a knee injury. Iguodala and McCaw being out means two wing players with defensive chops to throw at Chris Paul and James Harden aren’t available.

It’s not like Houston hasn’t dealt with its own adversity. Paul is dealing with a foot injury of his own, and Luc Mbah a Moute — a critical piece all season and a perfect weapon to use against Golden State — isn’t even playing after dislocating his shoulder twice this season and looking ineffective early in this series. But the Rockets are a truly great team, and one that was built to take on Golden State.

The Warriors are still favored to win this series, and they should go on to win a second straight title. But their roster construction left them in a position where, in the wrong matchup and if the wrong things broke against them, a team that shouldn’t have trouble because of its overwhelming top-end talent could have some.

The Rockets are that matchup.

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