Richard Thompson / Loudon Wainwright III, Knight Theater in Charlotte, 4/19/10

The house lights were still up when Loudon Wainwright III walked onto the stage. So he could see that the 1,200-seat Knight Theater, beautiful as it is, was maybe two-thirds full. I wonder how many times he and Richard Thompson, separately and together, have played to theaters of quiet but devoted fans with empty seats in the back, all their talent not enough to fill the house. Talent doesn’t always sell tickets.

But God almighty, the talent.

Wainwright is 63 now, Thompson 61, and there’s no need to feel sorry for them — they’ve been able to do what they love and make a good living it for something like 40 years apiece. But you hear Wainwright crack open his family secrets and spill them on the floor, or you hear Thompson rev up a guitar break as powerful and precise as a Ferrari running through the gears, and you wonder why they’re not playing arenas.

And then you’re glad they’re not, because it would never be this quiet and you would never get this close.

Here’s Wainwright, in a rare moment at the piano, singing about how he notices his kids like to sing in the same key. Here’s him in “White Winos” singing about his mom liked her white wine, almost (but not quite) to the point where she would let loose her anger about his dad. Here’s him in “Unfriendly Skies” trashing an airport official named Susie who cracked his precious Martin D-28, then wouldn’t let it on the plane.  (He calls her Susie because he doesn’t want to get sued. Then, in the next line, he lets slip that her name is Angela.)

He’s funny, heartbreaking, weird — he does a little Michael Jordan thing with his tongue in between verses — and worth the money all by himself.

But then Richard Thompson came on.

He played his bagful of alternate-universe hits like “Crawl Back (Under My Stone)” and “I Want To See the Bright Lights Tonight.” He absolutely killed a cover of Britney Spears’ “Oops… I Did It Again.” He filled every song with riffs and rolls and leads, always in service to the song, but at the same time proving that he’s one of the five best acoustic guitarists in the world.

And he played “1952 Vincent Black Lightning.”

If you know any Richard Thompson song, that’s probably the one — it’s on the setlists of a million folkies on open-mike nights, and iTunes shows me two dozen covers (I like the Mary Lou Lord version on “Live City Sounds,” recorded in a Boston subway station). It’s about a robber and the girl who loves him and the fine motorcycle they ride, and it’s tragic and epic and inspiring all tangled up in those six guitar strings and the way, at the end, that Thompson stretches out that last riiiiiiiiiiiiiide.

It was a performance strong enough for a million. About 800 of us got to see it. We went home lucky.