Chicago Symphony audiences have long since learned from Daniel Barenboim's many admirable Mozart concerto performances that this repertory often works best when conducted form the keyboard.

When you have another superior Mozart pianist Mitsuko Uchida, directing Mozart concertos from the Steinway, and doing so with such ease and infectious pleasure in making music as she displayed Thursday at Symphony Center, who wants (or needs) a separate conductor?

Uchida took charge of an all-Mozart programme created in the wake of guest conductor Charles Mackerras' having cancelled his appearances. Half of the CSO players were enjoying the night off, which made the Armour Stage look a lot bigger than usual. This fine-tuned the audience's ears to savour orchestral chamber music - a lovely respite from the heavy late-Romantic repertory they've been hearing in recent weeks.

Uchida has been busy directing Mozart concerto cycles from the piano bench with orchestras in Cleveland and Berlin. And she has recorded the entire set, triumphantly, for Philips. So she knew precisely what she was doing in both concertos she performed on Thursday - No 12 in A major K414 and No 19 in F major K459.

Both works offer 18th century elegance and charm in compact, unpretentious packages. Neither trades in the emotional complexities of the final eight concertos. Uchida was fully inside the music's style and spirit. Above all, her performances enforced an intimacy of scale and communication that heightened clarity of texture and emphasized the closeness of dialogue between the piano and various sections of the chamber-size CSO.

In neither concerto did Uchida dominate the musical interchange unduly nor upset the balance. Her playing - elegant, aristocratic but never simpering - suggested a first among equals rather than a soloist per se. She's a more subtle Mozartean than Barenboim, a difference that was most apparent in her 'Dresden china' approach to the Andante movement of the K414 concerto.

But the pianist's delicacy of touch was never achieved at the expense of naturalness or spontaneity, as her robust reading of the F major concerto proved. In its sheer wit and joie de vivre, the work looks ahead to the music of Papageno, the comic birdcatcher of Mozart's Magic Flute. Uchida led with arms thrusting upward, fingers quivering, as if she were emitting invisible sparks; in a quite magical way, she was.

One heard a polished, technically superb, finely blended and beautifully balanced account.