Bonnie Raitt’s stunning voice nearly obscured her guitar work at her split bill with Taj Mahal at Red Rocks on Sunday.

Nearly 40 years ago, Bonnie Raitt opened up for Taj Mahal. Sunday night at Red Rocks, Taj returned the favor, in a sense. Not that either of them need much in the way of favors, at least so far as their music career goes. Raitt has won nine Grammy Awards and has been flashing Girl Power since long before any Spice Girl sported that slogan. And pioneering bluesman Taj Mahal was big before you were born.

He’s still big — big, big voice, and now a body to match. Taj Mahal kicked off an unusually blustery August evening fronting his seven-piece band through an instrumental standard blues progression, as if leading the band through calisthenics, and then taking on Bo Diddley’s “Diddy Wah Diddy.”

Sporting a Kangol hat and a khaki jacket, Taj exudes cool sexuality as he always has, but now at age 66 he no longer has to do so constantly. A few well-timed flashes of physical propulsion do the trick. In classics like “Going Up to the Country, Paint My Mailbox Blue” and newer renditions of classics like “Farther on Down the Road,” he let loose with a frosty voice — holding a ten-second note on the latter — that mixed titillation with a bit of road-warrior savvy. He went down real easy.

Would it be too boorish to admit I never realized Bonnie Raitt played some of the wicked guitar lines she clearly does play? No, not because I don’t think a woman can play guitar (I could feel the outrage from Raitt fans rising before I finished that last sentence), it’s just that her voice and sass are so at the forefront, and the rough-road-to-riches story so central to the Bonnie Raitt narrative, that you don’t much think about it unless you see her in person.

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If it were 20 years ago, I’d have seen on MTV, and I’d know better, but then on the cover of “Nick of Time,” you can’t actually see the guitar — only the strap. Like the rest of you, I blame the media.

I wouldn’t make that mistake after seeing her take on some scorching solos, especially during her hit “Thing Called Love,” which featured an exquisite guitar back-and-forth between Raitt and George Marinelli. And yet, she was at her finest during her encore, in a jazz singer sort of role. On “I Can’t Make You Love Me,” she wrung every note, every syllable for emotional content. It was delightful.

After the individual sets by Taj and Raitt, they merged their bands onstage for a showcase dual set with 11 musicians, including two drummers (essentially doubling parts). Raitt and Taj have superb charisma on their own, and are infectious together — they’re friends, flirty and ferocious when they take on the microphone and each other. That said, they’re a few luxury tour buses removed from the blues. Their valedictory electric set together was fun and no doubt virtuosic, but also a bit self-congratulatory.

Taj Mahal and Bonnie Raitt perform Taj’s “Done Changed My Way of Living” on NBCs The Today Show – July 30, 2009. Taj’s new CD “Maestro” is amazing with guests: Ben Harper, Jack Johnson, Angelique Kidjo, Los Lobos, etc… He was just entered into the Blues Hall of Fame!

But they are a great pairing, as had been seen earlier in the evening. Midway through Raitt’s solo set, her band had left and Taj alone replaced them. For a few songs, including a rendition of Mississippi John Hurt’s “I’m Satisfied” in which intricate finger-picking merged with slide guitar, they hushed the crowd and showed it the fruits of 80 combined years of music-making. “It’s hard to turn a place like this into a little club,” Raitt said, “but I think we just did.”