Joshua Bell brings with him more than just a 1713 Stradivarius, superb technique, and incisive musical intelligence. He also draws a younger crowd. The average age on Tuesday evening at Avery Fisher Hall for his Mostly Mozart Festival concert was closer to 50 than the normal 75.

Mr. Bell’s performance of the Concerto No. 1 of Sergei Prokofiev was a decidedly mixed effort. While the period instrument crowd encroaches even further into the repertoire of the last century, sucking the life out of modernist melodies, Mr. Bell does just the reverse. He imbued the neo-Romantic themes of this piece with the most generous of vibrato, expounding on the opening material of the Andantino in a meltingly beautiful manner, and projecting a cantabile sound of extraordinary richness for the final Moderato.

There were, however, more than a few instances of uncharacteristic inaccuracy, particularly in the Scherzo Vivacissimo. Furthermore, and most disturbing, the solo performance was surrounded by a rather lackadaisical atmosphere. Energy flagged repeatedly, while Mr. Bell chose not to emphasize down-bow accents. Hardly ever playing above a whisper was a savvy necromancer’s trick to rivet our attention, but never letting loose the passion and fire of the composer was simply wrongheaded.

Mr. Bell was enabled in his pococurante approach by the assembled instrumental forces led by the Finn Osmo Vanska, who did a good job of presenting Prokofiev’s subtle colorations, but left out his sarcastic — some might even say sardonic — bite. The festival orchestra sounded rather flabby throughout. A listener has come to expect quite a lot from Mr. Bell (although perhaps not that much from the Mostly Mozart musicians), and would have every right to have been disappointed by this wayward realization. But, since it was Joshua Bell and his devoted audience, the ovation went on for a very long time.

The chicken and egg question of whether the violinist or the maestro was more responsible for the enervation of the Prokofiev was answered rather convincingly in a tired rendition of Beethoven’s Symphony No. 1. Mr. Vanska has a positively beatific reputation as leader of the Minnesota Orchestra, but his appearances at Mostly Mozart thus far have been short of Furtwaengler territory. When the courtside seats were new, he led a seemingly interminable version of Schubert’s “Great” C major Symphony, and now he is back with plodding, heavy-footed Beethoven. The orchestra struggled to achieve an occasional state of ordinariness. Otherwise, their phrasing and nonchalance produced an irritatingly singsong regurgitation of what should be a marvel of classical balance and grace.

Of course, Mr. Vanska is but a guest conductor, here for two nights and then gone. His allotted amount of rehearsal time is hardly sufficient to weave straw into gold. Since the festival is only four weeks in duration, and since the orchestra has many evenings off, wouldn’t it make more sense to have only the music director at the helm? Louis Langree initially improved this ensemble exponentially, but it has since plateaued at a significantly lower level. Perhaps consistent leadership can achieve excelsior.