The slack, perverse beauty of Liza Minnelli’s performance style in her heyday — that coursing vibrato shaking out of her body, those strutting gams and pinwheel-eyelashed orbs, the love-me-love-you intensity invested in every song — is the thrilling revelation that comes from watching Liza With a “Z” in its restored, digitally mastered form (airing Saturday at 8 p.m. on Showtime, and available on DVD April 4).

The legendary 1972 live concert created for television, but retired to the vault after only three airings — and a handful of awards — is a crazy/beautiful, highly addictive reminder of true performance magnetism in this age of frozen, canned-gesture tune-holders on American Idol and, frankly, most of the live musical performances one catches on awards shows and concert specials.

The swirl of genres getting the Bob Fosse–choreographed, Minnelli-belted workout — dirty rhythm rock (“I Gotcha”), vaudeville (“My Mammy”), sweet soul (“Son of a Preacher Man”), Broadway pastiche (“Ring Them Bells”), plus a showstopping Cabaret medley — is simultaneously heady and insane, but so rich in feeling, movement and hypnotic oomph that this show refuses to be merely a time capsule.

The only moment that pulls you out of phenom heaven and reminds you that this 26-year-old, imminent Oscar winner was in store for much personal heartache comes in her introduction to the Charles Aznavour–penned romantic lament “You’ve Let Yourself Go.” Having bemoaned the ubiquity of love songs about the bloom of new love, she sounds almost childlike-excited announcing, “This song is about two people who’ve already known each other for quite a while.” And it’s the only number from this tour de force night I’d almost prefer to hear her sing now — now that we’ve all known her, and all her ups and downs, for quite a while.

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