Though Willie Nelson is a seasoned veteran comfortably ensconced atop the pop music heap, he continues to push himself forward. Last night at Merriweather Post Pavilion, he radically reinterpreted his rich catalogue of songs to test his stronger bass vocal range, his ever- more unorthodox phrasing, his growing knack for substitute melodies and his increasing prowess as an acoustic guitarist. These gambles and their big payoffs made last night a revealing, rewarding experience, even for those who've seen his last three visits to the pavilion.

"Ain't It Funny How Time Slips Away," one of his earliest songs, took on a tone of wry resignation as he filled it with speechless pauses and quick, shrugged-off phrases. He kept the chords and rhythm to Kris Kristofferson's "Me And Bobby McGee," but completely revamped the melody. His inventions played against the listener's expectations to create a delicious tension. Then his acoustic guitar answered each vocal phrase with yet another melody.

Nelson's once large troupe has been pared down to a sextet that knows the value of not playing certain notes. Nelson took frequent and long acoustic guitar solos that whittled down melodies and rebuilt them instinctively with sharp intonation and Latin phrasing. The highlights of the two-hour set were the ballads. Nelson stated and restated the title lines, each time with a different melody and emotional nuance -- disappointed, then hopeful, then resigned.