The entire season of American Idol was building up to this moment.

Finally, the four best singers were pitted head to head. Any could go home. Any could win.

This four provided the first real sense of drama in the show’s history. It was kind of like the 2008 NCAA Men’s Basketball Tournament, when all the number one seeds faced off in the Final Four. Only this time, there was nobody from Kansas (i.e. David Cook) worth rooting for.

Think there’s a clear frontrunner? How much money would you be willing to bet?

The Idol theme was “rock night,” and rather than trotting out some old-timey concept of rock — say, Little Richard — the show actually chose a mentor who embodied the hard rock lifestyle: Slash.

The former Guns N’ Roses guitarist still looked the same, still played his Les Paul while peering through sheepdog bangs and still came across like he’s more comfortable lying on the floor of the Whisky a Go Go than sipping margaritas with Paula Abdul.

But there are rock stars … and then there are TV rock stars. Which would show up tonight?

Adam Lambert answered that question in a hurry, with a rousing rendition of Led Zeppelin’s “Whole Lotta Love” (which was actually recorded 40 years ago this week!).

His voice was certainly cut out for the upper-register “golden god” histrionics found in the Robert Plant lead. Like the original, the song was short on melody but long on attitude. Despite the fact the judges gushed on about Lambert being a “true rocker,” he’s encountered a much harder time this season shedding his Broadway persona on legitimate heavy tracks. The jury is still out on whether he managed to fully succeed on this Zep classic.

Young, young, young Allison Iraheta attempted to blend her blues-rock delivery with a blues-rock artist. She chose to emulate Janis Joplin with “Cry Baby.” She succeeded in showing off her vocal tone and control, but also revealed the main flaw in Joplin’s arsenal: the artist wrote and performed a bunch of crappy songs. Great voice, amateurish material.

The season’s penchant for retooling its format was unveiled through the latest attention grabber: a duet performed by Kris Allen and Danny Gokey. The pair chose “Renegade,” one of the stronger cuts from the Styx repertoire. It was in many ways the best-sounding song of the night, with the house band coming across tight and aggressive. Though neither of the pair’s voices quite fit the song, their harmonies together were stellar.

Allen had to regroup, strap on a guitar and deliver the later Beatles hit “Come Together.” The choice seemed fine on paper, but the actual delivery was disappointing. It’s not exactly a singer’s showcase, with its mouthfuls of random, meaningless lyrics (according to composer John Lennon himself) splayed over a fairly standard variation on a blues progression. Not terrible, just forgettable.

Gokey had the unenviable task of condensing Aerosmith’s four-and-half-minute “Dream On” into a 2-minute non-epic. Like Michael Johns before him, who famously delivered a similarly castrated version of The Beatles’ “A Day in the Life,” Gokey didn’t afford himself enough time to subtly build up to that crowning end wail. Overall, it seemed rushed and unconvincing.

QUICK KARA DIOGUARDI FAUX PAS: In her criticism of the song, she mentioned Gokey should sing “an earlier Aerosmith song, like ‘Crying’ or ‘Crazy.” “Dream On” was actually the first single on the band’s first album in 1973. The others she mentioned both were released in the ’90s.

Lambert and Iraheta returned for a duet of Foghat’s “Slow Ride” (would have never guessed that pick). The evening ended on a great bit of dumb rock energy, with each belting out their guts with reckless abandon. Not everything about the night rocked, but at least this duet left the impression it did.

Bottom three prediction: Allison Iraheta, Danny Gokey, Kris Allen.

Loser: Honestly, I have no idea. But let’s say Danny Gokey for grins.