There was a moment near the end of Monday's "Austin City Limits" taping at ACL Live when Willie Nelson seemed to pause for a moment and take it all in. He'd just finished "On the Road Again," but before he followed with "Always on My Mind," he gazed lovingly upon the crowd, which roared with appreciation. We all knew what we were witnessing. He did, too.

Judging solely from the set list and the personnel, you might have thought this was just another night with Willie — and in some ways, it was. Running through about two dozen songs in a little over an hour, joined by the five-piece Family band that always has his back, Nelson did what he does night after night, all across America.

But on another level, this was special, something you could feel in the room from the opening strums of "Whiskey River." Forty-four years ago, Willie Nelson jump-started "Austin City Limits" in the pilot episode, and there's a mutual respect between the show and the man that is intimately understood. Thus it was fitting that his 18th appearance on the show had no frills, no guests, no tailored set list. The taping simply documented Willie as-is, because he IS "Austin City Limits."

He was also on-point all night long. The last time he'd done a full episode of the show was almost a decade ago with Asleep at the Wheel, and it had been a full 15 years since he'd done one with his own band. Will there be another? Quite possibly not, and it felt like Willie wanted to get this down right for posterity, and history.

We got the medley of classics that established him as a songwriting legend: "Funny How Time Slips Away," "Crazy," "Night Life." We got the instrumental numbers that showcased sister Bobbie Nelson's piano ("Down Yonder") and Willie's trusty guitar Trigger ("Nuages"). We got the dedications to departed pals Waylon Jennings ("Good Hearted Woman") and Merle Haggard ("It's All Going to Pot"). We got the pinnacles of his artistry as an interpreter ("Georgia on My Mind") and as a songwriter ("Angel Flying Too Close to the Ground").

At 85, Willie's wise enough to know his voice is weaker than it once was, so he calls out often for the crowd to join in, and they reply with joy and respect. "I hear it!", he answered back with a grin on the second go-round in "Good Hearted Woman," just one of many sing-along moments for the audience. Their reward was the occasional trademark red bandana tossed to the standing-room throng in front of the stage.

Whatever his vocal challenges, as a guitarist Nelson seems to get even more fascinating with each passing year. His runs dodging the tempo on "Still Is Still Moving to Me," the fascinating interplay with sister Bobbie's piano on "Nuages," even his sly little "Jingle Bells" tag at the end of "Night Life" all revealed an artist who's still exploring, still playful, still pushing the boundaries of where his music can go.

Bobbie at stage right and harmonica master Mickey Raphael carried the melody when Willie wasn't leading it with Trigger, leaving the rhythm section of bassist Kevin Smith and sibling drummer/percussionists Paul and Billy English to walk that fine line between country and jazz behind them. Willie gave them first-name-only introductions midway through the night; they might as well all be Nelsons, given how much this band is Family not just in name.

Waving farewell after a rousing, standing-room, hand-clapping finale of "Will the Circle Be Unbroken" and "I'll Fly Away," Willie smiled wide as Texas and declared with all sincerity, "Thank you, Austin City Limits!" The band played on as he exited stage right, and everyone within the city limits of Austin knew that they could never thank Willie Nelson enough.

• READ MORE: Check out our extensive Austin360 coverage of Willie Nelson