After hearing a piece played by scores of soloists from myriad eras and traditions, it's rare that a performer can tell you something new. But so it was with Christian Zacharias, whose performance of Beethoven's Fourth Piano Concerto highlighted an otherwise lackluster afternoon at Tanglewood Sunday. Zacharias gave such a spirited reading of the concerto's finale that the audience rose almost immediately with the last chord.

Somehow energized after a second movement that lacked much cohesion of thought between the soloist and orchestra, Zacharias dove into the finale with visible enthusiasm. He slammed his powerful left hand into the bass line during at least two tuttis, and practically cued the cellos himself during the recapitulation. He pushed every beat with an ardor that made up for his interpretation's lack of spaciousness.

Upon finishing, he shook visiting maestro Jeffrey Tate's hand several times with noticeably more than the usual gratitude. It was refreshingly clear that the overwhelming Zeal Zacharias conveyed came from the most unassuming of sources, not from any desire to steal the show.

Not that Zacharias began so auspiciously--his first movement sounded more like a walk in the park than the heartfelt and dignified statements of Schnabel, Kempff or Fleisher (though, to be fair, he stoked some embers in the cadenza that turned to flame in the third movement.) And not that the Tanglewood audience had attended so many concerts--they clapped sheepishly after the first movement, and many elderly among the crowd could be heard talking, giggling or loudly removing the plastic wrap from hard candies during the performance.

And finally, not that the BSO was pitching its best stuff on Sunday. In the opening Serenade by Elgar, the strings played sweetly enough but without any of the alternating tension and expansiveness demanded by Tate. The first violins never broke through a stifling false refinement--perhaps they're not used to a conductor so passionate as Tate. The seconds, ironically, showed much more emotion than the firsts in the crucial middle movement.

The basses set an appropriately crisp beat in the Beethoven and later in Brahms' Third Symphony, but no other strings showed any desire to match their attention. Adding embarrassment to injury, the first violins and cellos clearly faked several sections in the first movement, including the arpeggios that accompany the main theme.

Even less can be said in favor of the brass. Muffled and shy in the Brahms, the entire horn section produced less power than any single counterpart of the legendary Chicago Symphony Orchestra of the 1970s. This absence of inspiration was particularly disappointing in the finale, but by this time Tate had ceased trying to goad the BSO to action. Whether from frustration or disinterest, his take on the Brahms offered few surprises in phrasing and even fewer variations in dynamics and tempi. Only the mellifluous soli of the winds merited much remembrance.

The BSO appears to have reached another crossroads in its relatively young history. Its players are certainly capable of vibrant, intense performances: this reviewer heard Bernard Haitnik dispel their complacency only a few years ago in the same Tanglewood Music Shed. Such revelations, however, come far too infrequently. Under Munch, Monteux, and Leinsdorf, such revelations came weekly.

Whether a consequence of its direction or its membership, the BSO's loss of vigor warrants quick and decisive steps. Too bad, then, that all the possible culprits will remain in their seats until retirement or death. Until then, Boston can only watch as the showpiece of an alleged "city of culture" continues its decline.