Keith Jarrett explained to the SRO Kennedy Center Concert Hall crowd last night that his solo piano improvisations were a process of conscious risk-taking. He proved his point. His opening 45-minute piece took many risks and failed most of them. The piece was a tedious series of vague reveries and unconnected phrases that never coalesced into any structure but random or any mood but indulgent.

After intermission, though, Jarrett returned for a half-hour tour de force that showed him winning both technical and conceptual gambles with impressive boldness.

The 37-year-old Pennsylvania pianist made his name in mainstream jazz but has recently moved toward a more classically influenced pastoral music. His first piece revealed the pompousness that his classical excursions often lead him into. He lingered too much over slow, dreamy phrases and pregnant pauses.

The second piece leaned more toward his jazz background and began with a modified boogie-woogie. This rhythmic structure provided the skeleton for the flesh of his marvelous melodic improvisation. He gathered a momentum that kept him going past possible digressions. His left hand pushed the tempo with jagged, impatient note clusters, and his right searched impulsively for ever newer harmonies.