Fournier, following his impromptu duet with Paul Simon. (Kristin Mowry)

Whatever kind of trouble you might get into in Washington, there’s a lawyer here who can help.

Midway through his Constitution Hall show Wednesday night, Paul Simon seemed to have difficulty remembering the words to his song “Gumboots.” A fan in the front row shouted out the first lines. He was Paul Fournier, a 42-year-old patent attorney in a blue button-down shirt.

“Well, why don’t you come up and sing it?” asked Simon.

Fournier clambered onstage and delivered a nearly note-perfect rendition of the song, joined by Simon on the chorus — and pretty much stole the show, reports our colleague Joe Heim.

Heim caught up with an exuberant Fournier after the show. A fan since pre-school, when his parents made him listen to “I Am a Rock” and “Bridge Over Troubled Water,” he said he’s been a serious devotee since the Concert in Central Park era of the 1980s and just naturally knows all the words. And no, this wasn’t a set-up, he said.

It’s not the first time Simon has leaned on a fan for backup: Earlier this month, when a woman at his Toronto concert requested the song “Duncan,” and explained that she’d used to teach herself guitar, Simon brought her on stage to play it. Unclear how often he does this kind of thing; we’ve heard anecdotes of Billy Joel and Green Day pulling unsuspecting audience members on stage to take over the instruments or mike.

Fournier never saw it coming. The attorney with Drinker Biddle & Reath said he only looked out at the audience once or twice during his moment in the spotlight to soak in that feeling – but mostly kept “focused on the performance to make it sound as good as I could.”

“At one point I believe he harmonized with me,” he said. “It was an amazing experience.”

Click Track: In concert: Paul Simon at DAR Constitution Hall reviewed

YouTube: Fan joins Paul Simon on stage in D.C.