Megadeth & Motörhead The Pearl, April 17.

Two very different heavy metal legends co-headlined at the Pearl on Thursday night. Motörhead frontman Lemmy Kilmister is the closest thing to the Johnny Cash of metal, a universally beloved, hard-living trouper who continues churning out new material despite health problems and advancing age. Motörhead have had to cancel numerous tour dates in the last year or so thanks to Kilmister’s health, and the 68-year-old seemed a bit weak as he slowly walked onstage, standing pretty much in the same spot for the entirety of the band’s hourlong set. His voice lacked its typical ferocity, too (the standard intro “We are Motörhead, and we’re going to kick your ass” sounded unconvincing), but it picked up as the set wore on, and by closers “Ace of Spades” and “Overkill,” he sounded nearly like his old self, even if he didn’t quite look it.

If Kilmister is heavy metal’s beloved grandpa, then Megadeth’s Dave Mustaine is more like its slightly disreputable uncle, who’s garnered more publicity in the last several years from his right-wing politics and promotion of conspiracy theories than from his music. Still, there’s no denying the greatness of Megadeth’s contributions to metal, and Mustaine wisely stuck to material from the band’s ’80s and ’90s heyday (aside from one new song). Megadeth played only about 10 minutes longer than Motörhead, but the crowd clearly treated them as the main attraction, and the band’s performance lived up to those expectations. Mustaine is still a monster on the guitar, and he was well-matched by fellow guitarist Chris Broderick on songs like “In My Darkest Hour” and “Tornado of Souls.” A guy dressed as band mascot Vic Rattlehead took the stage for main-set closer “Peace Sells,” bringing some welcome goofiness to what proved to be a night of intense metal.