Adam Lambert, left, and Brian May of Queen perform at Merriweather Post Pavilion. (Kyle Gustafson/For The Washington Post)

Adam Lambert is the latest in a line of Freddie Mercury fill-ins to front Queen in the last couple of decades. (Elton John, Robbie Williams and Paul Rodgers came before him.)

At 32, he’s also the youngest, and the May-December aspect of the alliance was impossible to ignore during Sunday’s Merriweather Post Pavilion show whenever he stood next to drummer Roger Taylor, who turns 65 this week, or guitarist Brian May, now 67.

But somebody’s gotta sing these songs. A 2006 survey rated Queen’s first greatest hits collection as by far the greatest-selling record in England’s history; press materials for the current tour claim that it can be found in “one in three British households.” (That poll also ranked Queen’s “Greatest Hits II” as the seventh-biggest British album of all time.) And Lambert is likely the best choice out there. His fame came via a second-place finish on “American Idol” in 2009, and in the season finale, he performed “We Are the Champions” alongside Taylor and May. He still seems a little shocked by his hiring as Mercury’s stand-in, however.

“I’m onstage with Queen!” Lambert squealed, after getting up from the lavender couch he sprawled all over while crooning “Killer Queen,” wearing the second of many leather-spike-sequined ensembles he’d sport on the evening. Mercury was far more than just a singer, and early in the show, Lambert occasionally stumbled when trying to entertain the fans in nonmusical ways. He spit a drink on the crowd awkwardly, and he didn’t seem comfortable introducing “Fat Bottomed Girls” with a crude and not-safe-for-work order for large females in the crowd to dance.

But Lambert showed he could handle the rockier passages in the Queen songbook, and he got the huge crowd jazzed by belting out “Tie Your Mother Down” and “I Want It All.” Lambert ended “Somebody to Love” with the sort of Christina Aguilera-like, multi-octave blitz that helped him catch Simon Cowell’s eye and ears back on “Idol.”

Lambert, 32, is the latest in a line of Freddie Mercury fill-ins to front Queen. (Kyle Gustafson/For The Washington Post)

Lambert led his elders on “Another One Bites the Dust,” the pop dance tune that was the band’s biggest-selling U.S. single. It was written by Queen’s original bassist, John Deacon, who has declined to join any of the band’s tours since Mercury’s 1991 death from AIDS complications.

Lambert was occasionally subservient, however. He went backstage a few times as May came front and center. May is viewed as having one of the bigger brains in rock; his PhD thesis in astrophysics is titled “A Survey of Radial Velocities in the Zodiacal Dust Cloud.” He briefly tried explaining Einstein’s theory of relativity to the crowd before leading the singalong on the folkie time-travel tune “39.” Less brainy was May’s decision to walk around the stage alone, save for his guitar, lasers and smoke, for a brutally long solo that started off stagnant and remained inert. Fans could rightly wish for a time machine to get back the 15 minutes or so they’d spent watching that.

The show also flagged as a result of other non-brainy staging decisions. Neil Fairclough, Deacon’s understudy, was given a bass solo while others left the stage. He’s likely a fine musician, but it’s even likelier that no more than a few of the folks who showed up could even name him, and likeliest that even fewer wanted to see a bass solo. Momentum flagged again when Taylor moved to a second drum kit so he could do a percussion duet with his son, Rufus Taylor.

Lowest of all, “Bohemian Rhapsody,” the prototype Queen song, was hardly given its due. The tune’s inclusion in the 1992 film “Wayne’s World” allowed secret Queen lovers everywhere to start belting out this operatic bombast whenever it came on the car radio. But on this night, half of “Rhapsody” was played via a pre-recorded video shown on the amphitheater’s big screens. The live bodies returned in time for May’s gargantuan outro guitar solo, but that staging still turned what should have been a home run into a ho-hum.

Things picked up one last time when Lambert came out for the encore of “We Are the Champions,” sporting a glittery crown on his head. Hail the new king of Queen.

McKenna is a freelance writer.

An earlier version of this review had an incorrect name for Queen’s drummer. This version has been updated.