John Mayer may have developed an early reputation as the sensitive, acoustic-backed singer/songwriter whose “Your Body is a Wonderland” scored a Best Male Pop Vocal Grammy in 2003. But the Berklee-trained musician’s heart has always been in the electric blues of
early musical hero Stevie Ray Vaughan, influences that have seeped steadily into Mayer’s own music in recent years. Here’s Mayer proving the point at a Houston gig in early August, turning in a version of “Mercy” with some crowd-pleasing showmanship that would have done T-Bone Walker proud.