One-time Oscar winner Matthew McConaughey is famous for his catch phrase, “All right, all right, all right.” Six-time Grammy winner Dr. John is so cool he needs only one “All right.” During his shows, he says it sparingly after this or that song.

Saturday night in Repentance Park — the downtown green space between the Old State Capitol and the River Center — Dr. John and his Nite Trippers played their much-anticipated and appreciated headlining show at the Baton Rouge Blues Festival.

Getting Dr. John, a Rock and Roll Hall of Fame inductee whose music history stretches to 1950s and ’60s New Orleans rhythm-and-blues and rock ’n’ roll, was a Blues Festival coup. During his post-sunset show featuring his classics, New Orleans standards and songs from his Grammy-winning 2012 album, “Locked Down,” the physician of funkology and many other styles did not disappoint.

Singing in characteristically grainy tones and playing piano- and electric keyboard, Dr. John and his band got just about everybody moving. It was a big, happy crowd.

There’s something to be said, too, about the Blues Festival’s zero cost of admission. In recent years Dr. John made regular visits to the Manship Theatre. But as fine a venue as the Manship Theatre is, its 325-seat capacity means tickets for concerts there ain’t cheap.

Bringing Dr. John to the free Blues Festival allowed so many more people into his tent. His Blues Fest audience covered the Repentance Park grass and filled overlooking steps and walkways alongside the park.

New Orleans music being so deeply connected to Mardi Gras, Dr. John threw a few Mardi Gras songs into his wide-ranging show. The fun began with an infectious “Iko Iko,” originally titled “Jock-A-Mo.” Another singer-pianist from New Orleans, James “Sugar Boy” Crawford, wrote “Jock-A-Mo,” combining two Mardi Gras Indians chants into the song that he released in 1953.

The Carnival time vibe returned later with another Mardi Gras essential, the Dr. John-composed “Big Bass Drum (On a Mardi Gras Day).” And music by another Mardi Gras-linked artist, Professor Longhair, arrived by way of Dr. John’s faithful and, of course, grooving, rendition of one of Longhair’s piano masterworks, “Tipitina.”

Dr. John reached back to his 2001 album, “Creole Moon,” for “Food for Thot,” rapping the song’s topical lyrics over hard-funk music. Latin rhythm propelled Dr. John’s take on “St. James Infirmary,” another New Orleans standard. “I’m go’ play a little bit,” he said before hitting one of his many piano solos of the night.

In something of a surprise, Dr. John gave an intimate performance of Ray Charles’ “Tell Me You’ll Wait For Me.” The song cast the 73-year-old musician in the unusual role of romantic balladeer. He pulled it off beautifully.

Moving to his reedy-sounding Nord keyboard for “Locked Down,” Dr. John fit naturally into yet another music genre, garage-rock. At the Nord keyboard again, he struck the instantly recognizable opening riffs of his biggest hit, the always funky and trippy “Right Place, Wrong Time.”

The piano-based charmer “Such A Night,” also from 1973s “In the Right Place” album, ended the show, as Dr. John might say, in a “mos’ scocious” way.

Down to a four-piece band for his Blues Festival appearance, Dr. John dedicated “Such a Night” to his absent music directress and trombonist, Sarah Morrow. Late Saturday night, Morrow tweeted that she’s been in the studio all week, mixing Dr. John’s new album, a tribute to Louis Armstrong.