OTTAWA - Bonnie Raitt gave thousands the middle-finger last night and we thanked her for it.

Raitt, you see, reserves her right middle-finger for a slide, the tubular glass object that for 35 years has been as much a part of the veteran singer's distinctive sound as her trademark rasp. Most guitarists favour the pinky. Raitt is not most guitarists.

Nor has the politically conscious one been one to follow convention. Hence, while all around her are bringing everything but blues to City Hall, Raitt made a point of "whipping out a few songs I don't usually play," for the occasion.

Even when turning to the pop-rock material that made her a household name some 18 years into her career, Raitt rarely strayed far from her blues roots. A rendition of her Nick of Time hit, Thing Called Love, was dutifully given a slow and sexy treatment. That album's title track gained world-weary poignancy from a dedication to her now-late parents.

Dropping the names of mentors and peers, from blues pioneer Sippie Wallace to The Fabulous Thunderbirds, Raitt presented an inspired lesson in blues history, in a career that will soon span four decades.

The voice and the playing have never been better; Raitt knows that a blues performer only gets better with age. Her seasoned band -- keyboardist Jon Cleary, guitarist George Marinelli, bassist James Hutchinson and drummer Ricky Fataar, give or take the Texas Horns -- made it that much easier to make the point.

Raitt has always been a fighter. (And she still recognizes the empowering value of saucy remarks, like inviting the horn players to "come out and get horny on me.")

It took her nearly 20 years of should-have-been-hit albums to arrive at the enduring 1989 breakthrough Nick of Time. By that point, blues were an influence rather than a mission but she has never forgotten her roots. And she has never forgotten those who helped her to arrive.

That was evident by frequent nods to her band, and by the still-pretty-in-purple headliner's appearance alongside Keb' Mo' at the close of the fellow L.A. blues artist's opening set. (Keb' Mo' would later be brought out during Raitt's set.)

The set of the man born Kevin Moore was more about rhythm than blues, taking us not so much to the Crossroads he visited as Robert Johnson in the documentary Can't You Hear the Wind Howl, as to Memphis.

On his own, Keb' Mo' has developed a reputation as a modern-day incarnation of Johnson, Charley Patton and other early bluesmen. In the company of a five-piece band, the volume turned up, the frontman preferred to take us to soulville.

And he did it well, cleverly giving us a taste of material from throughout his eight-album career.

The highlights came when the guitarist (and he plays a mean slide too, for the record) brought us back to his 1994 self-titled debut album.

Keb' Mo' channelled the spirit of Otis Redding during a spine-tingling rendition of the ballad Don't Try to Explain. Later, at the close of the set, he let the band sit out a fine acoustic performance of Every Morning.

Of course, it helped that he had the woman with the powerful middle-finger to his right.