B.B. King knew what this review was going to say before it was written.

"I better get back to work," the 81-year-old blues man said while sitting on stage at the Keswick Theatre on Tuesday, his trusty guitar Lucille resting on his right hip. "Or else I know what it's going to say in the paper: Old B.B. was pretty good. But he talked all night."

That he did. Truth be told, when King wasn't making light of his physical ailments (diabetes, a "bad back, bad knees, and a head that's not much good either") and instead focused on actually playing music, he was better than pretty good.

Even as an octogenarian, he's a melismatic singer with plenty of vocal power. And as a guitarist - as influential as any who ever lived - he still plays with effortless mastery, whether he's tossing John Lee Hooker-style fuzztone boogie runs into the U2-penned "When Love Comes to Town" or simply picking out the melody in "You Are My Sunshine."

But at Tuesday's Keswick show - another was scheduled for the Glenside theater on Wednesday - the tuxedoed entertainer spent too much time calling the audience's attention to his admittedly excellent eight-piece band ("Mr. Stanley Abernathy, on trumpet. Make him happy!"). And too much time telling Viagra-Levitra-Cialis dirty-old-man jokes.

One highlight was a moving "Key to the Highway," on which he spoke the final lyric ("I'm going to do this until I die") as if it were a promise to himself that could never be broken. But King relied too heavily on playing truncated versions of his songs for laughs, rather than mining them for their inherent emotional power.

Case in point: After dismissing the four-piece horn section, he appeared to get serious, bending each note on the intro to "I Got a Mind to Give Up Living" with deep feeling. But he punctuated the line "And go shopping instead" with a big grin, and pregnant pause, to make it seem like the song was about a trip to the mall, rather than the morbid impulse to "pick out a tombstone, and be pronounced dead." The crowd laughed along with King, and the intensity of the moment was lost.

With a six-decade career at the top of his profession that's unmatched in blues (or any other pop-music genre, for that matter), and a concert schedule that would make a rock star in his prime wilt, the King of the Blues has more than earned the right to take it easy and get by on shtick every now and again. This was one of those nights.

Contact music critic Dan DeLuca at 215-854-5628 or ddeluca@phillynews.com. Read his recent work at http://go.philly.com/ dandeluca.