Bob Dylan is 71, and on recent tours, time seemed to be catching up with him. The voice has deteriorated steadily, he no longer plays the guitar much while reportedly struggling with arthritis, and his demeanor has occasionally bordered on indifferent, if not hostile. Despite playing to a two-thirds full United Center on Friday, he performed without video screens (unlike just about every other arena performer you could name) to bring the action closer to the folks in the balconies.

But Dylan mustered his "A" game for this concert, or as close to "A" as he can get anymore. No, the voice has not suddenly undergone a transformation. But he was singing with more spirit and clarity than I'd seen in years. He opened with a fierce blues instrumental, leading his crack six-piece band on guitar. Then he settled in behind a grand piano and the real action began.

Dylan has mostly been confining himself to electric keyboards on recent tours, and his contributions on the instrument have been muted, if not inaudible. But on the piano, Dylan was a force. Many of the songs were reconfigured in a way that places Dylan's voice and hands squarely at the center, and his playing was extraordinary – a dollop of barrelhouse boogie, some sanctified gospel chords, and a whole lot of Mose Allison-style blues-based improvisation and embellishment.

Early on, opener Mark Knopfler abetted the guitar front line of Charlie Sexton and Stu Kimball, embroidering Dylan's piano on "To Ramona" and jaunty harmonica on "Things Have Changed." Dylan deferred to his guest, pointing his pistol finger at Knopfler to signal another solo. The singer, legs splayed and leaning back, looked ready to bust out a few dance moves on "Tangled Up in Blue." Then as the song wound down, he moved to piano and brought it to a rollicking close – you could feel the energy level lift. Dylan donned a flamenco hat in tribute to "Blind Willie McTell," and brought the song surging back to life twice with his harmonica solos.

When Knopfler exited, Dylan reclaimed his "To Make You Feel My Love" from Adele, a hint of vibrato exposing the thinness of his voice even as it underlined the song's vulnerability. Then drummer George Recile – a monster all night with his steady-rolling river of groove – and bassist Tony Garnier locked into "The Levee's Gonna Break," and the show found its footing. Dylan turned his piano into an orchestra: rumbling, jazzy dissonance; terse counterpoint fills underneath his vocals; thundering gospel chords as prelude to spider-walking flourishes with both hands. In the process, he destroyed the rather tepid studio version of the song on the 2006 "Modern Times" album.

Similarly, he turned the piano into the foundation of a retooled "Desolation Row" and stoked a ferocious "Highway 61 Revisited" and a barreling "Thunder on the Mountain" with percussive left-hand bass lines. Only "Like a Rolling Stone" came off as a little flat in its new arrangement, though not for lack of trying – at one point, Dylan injected the classic with a reggae vibe.

Not everyone likely appreciated how Dylan tampered with his classics. Others may have been disappointed that he ignored his excellent recent album, "Tempest." Yet, by now it should be apparent to anyone who has followed Dylan's career that the singer may not remain forever young so much as forever restless. He treats his songs as portable, mutable works in progress – forever subject to change. On this tour, he's revealed himself to be a room-wrecking piano-player, equally at home in the saloon or the church. Even at this late stage, he makes it impossible to write him off, take him for granted or embalm him in his own history.

greg@gregkot.com

Bob Dylan's set Friday at the United Center:

1 Blues instrumental

2 To Ramona

3 Things Have Changed

4 Tangled Up in Blue

5 Blind Willie McTell

6 Make You Feel My Love

7 The Levee's Gonna Break

8 Desolation Row

9 Highway 61 Revisited

10 Forgetful Heart

11 Thunder on the Mountain

12 Ballad of a Thin Man

13 Like a Rolling Stone

14 All Along the Watchtower

Encore:

15 Blowin' in the Wind