PORTLAND — Willie Nelson is still playing his beat-up guitar and still thrilling crowds with his weathered old voice.

Nelson, 77, played a sold-out show at Merrill Auditorium on Wednesday night, and impressed with his deft handling of his Martin guitar, which he has named Trigger in honor of Roy Rogers’ horse. Nelson has been playing that instrument so long and so hard, he’s worn a hole clear through the wooden body.

At an age when many musicians turn picking duties over to younger gun-slingers, Nelson has done just the opposite. In the stripped-down band that he is currently touring with – sister Bobbie on piano, Bee Spears on bass, Mickey Raphael on harmonica and a tandem of Paul and Billy English on a single snare drum – Nelson is the band’s sole guitarist.

On many occasions Wednesday night, he proved that his most lasting genius may well be his ability to pick and play with the best of them. On “Still is Still Moving to Me,” he stylized the song with jazz trappings. His finger-picked tight lines throughout his “Funny How Time Slips Away” medley, and blazed his way through a high-octane version of “Me and Bobby McGee.”

The show felt very much like an American song book tour. Nelson played most of the songs that his fans wanted to hear, while covering material by Kris Kristofferson, Billy Joe Shaver, Steve Goodman, a host of tunes by Hank Williams and several traditional gospel numbers.

In all, he burned through 32 songs in just a little more than 90 minutes. At times, the concert felt hurried. Nelson barely paused between songs and only occasionally spoke with the crowd – and he performed mostly fast versions of the songs. Many lasted less than two minutes each.

The show also felt a bit formulaic at times, with Nelson handing off solos first to sister Bobbie and then to Raphael and then closing them out himself. After a while, they began to sound and feel the same.

But Nelson did not give a cursory performance, by any means. He worked hard, and played his instrument exceptionally well most of the time. He was a joy to watch.

He also sounded pretty good in his voice. He has always half-sung, half-spoken his way through his songs, adopting a jazz-influenced, almost improvisational approach to vocals. That said, he demonstrated that he is still capable of belting out a song.

The highlights of the evening were many: “Help Me Make it Through the Night,” which sounded tender and sad, accented with a gorgeous harmonica solo by Raphael; a spare version of “Georgia on My Mind,” featuring Spears on acoustic bass; and a fantastic version of “Georgia on a Fast Train,” in which Nelson nailed the clickety-clack lyrics perfectly.

The goose-bumps moment came mid-set, when Nelson delivered “Angel Flying Too the Ground” and “You Were Always on My Mind.” Neither song sounded much like the versions we have come to know over the years, but no matter: Nelson held back, slowed the tempo and concentrated on finding the appropriate pace and exactly the right delivery to make each song soar.

If the show had any flaws, it was simply that Nelson seemed bored with some of his most popular songs. There were too many sing-alongs with the audience and too many cursory run-throughs of songs like “On the Road Again,” “Good-Hearted Woman” and “Mamas Don’t Let Your Babies Grow Up to Be Cowboys.”

But the audience loved him. They gave him a standing ovation the moment he walked on the stage to begin the show, and sent him off onto his tour bus with another big standing-O. Nelson hung around the front of the stage at the end of the show for a solid five minutes to shake hands and sign autographs.

It was a generous performance and a nice gesture from an icon of American music.