No Army cadet can possibly work as hard as the young members of the corps de ballet did Wednesday night. From the moving opening scene of Balanchine’s “Divertimento No. 15,” eight women’s elegant arms gracing the air in perfect harmony, to the hourlong extreme athleticism by the entire corps (and most of the company) in William Forsythe’s killer “Artifact Suite,” it was time to recognize and treasure the humble foot soldiers.

Always nameless (until now), seldom noticed (except when something goes wrong), corps members such as those eight in the divertimento should have their day in the sun. Bravi to Dores Andre, Maureen Choi, Courtney Elizabeth, Dana Genshaft, Shannon Roberts, Lily Rogers, Jennifer Stahl and Courtney Wright. Yes, the eight soloists in Balanchine’s work were also excellent (especially Nutnaree Pipit-Suksun and Elana Altman), but they are used to accolades.

Being tried, true and famous is no guarantee of success, however, as George Cleve and the ballet orchestra turned in an uncertain, weak performance of Mozart’s music; at times, half the violin section seemed to quit playing altogether. The rest of the evening had tape accompaniment, except for Margot Kazimirska’s heroic (and amplified) playing of a typical Forsythe-percussive score, by Eva Crossman-Hecht.

Strange and haunting accordion music, by Maurice Pacher, served as the basis of Jacques Garnier’s “Aunis,” danced with stormy bravura by Rory Hohenstein, James Sofranko and Garrett Anderson (stepping in for Joan Boada).

The Forsythe revival, from last year’s U.S. premiere here, got the same reception as at prior performances: dozens departing from the audience halfway through the piece, those staying shouting bravi at the end. Although carrying the usual Forsythe signatures — bare, fully-opened stage, plain leotards, dazzling (occasionally blinding) lighting, twice the length of a typical ballet, a huge cast in constant motion or creating painterly tableaux — “Artifact Suite” is newly challenging and fascinating. Add to that “startling,” as the fire curtain is dropped repeatedly, and loudly, unexpectedly and midmovement.

With Muriel Maffre “conducting” the company in intricate, mesmerizing motions, Katita Waldo a standout among principal dancers, a real — not the capricious fire curtain — came down to mark the first half of the piece. However, as the Bach solo violin piece continued in the background, and house lights came up halfway, and in the ensuing five-minute break (or transition?), most of the audience defectors took their leave.

The departed missed a great deal, beginning with an unforgettable scene after the curtain rises. On the dark stage, units of the entire company swirl in strange patterns, groups meet, coalesce, part, come together again. The events, configurations, inventions, intensity and surprises of “Artifact Suite” add up to an unforgettable dance experience. Just don’t give up too soon.

San Francisco Ballet Program One

Where: War Memorial Opera House, 301 Van Ness Ave., San Francisco

When: 2 p.m. Sunday, 8 p.m. Thursday, 2 and 8 p.m. Feb. 10

Tickets: $10 to $205

Contact: (415) 865-2000 or www.sfballet.org

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