They started out playing boogie for bikers before charting the course for what would become known as “yacht rock.” Now the Doobie Brothers have granted a ’70s music fan’s wish by bringing the signature vocalists from both eras together for a 50th anniversary tour. As an indication of demand, Michael McDonald and Tom Johnston are sharing the stage at Zappos Theater inside Planet Hollywood Resort for an extended run.

This had long seemed improbable. McDonald had no reason to divert from his successful solo career. Johnston had overcome the decline in health that led to his leaving the band in the mid-’70s and resumed touring with the Doobies in 1987. There was no animosity between the singers, so all that really seemed to matter was if McDonald wanted to help celebrate the golden anniversary of the group that made him famous.

He agreed before plans were put on pandemic hold. In the ensuing time Johnston, founding member Patrick Simmons and McDonald-era multi-instrumentalist John McFee hit the studio to record the latest Doobies album Liberté, which was released last year. Johnston and Simmons also prepared the band’s autobiography, alternating chapters as they told the tale of The Doobie Brothers. (Long Train Runnin’ was set to be released three days before the beginning of the Las Vegas engagement.)

Johnston and fingerstyle guitarist Simmons co-founded the band in 1970, becoming popular on Northern California’s live circuit and a favorite of the Hells Angels. The name, inspired by slang for a cannabis joint, was meant to be permanent but was locked in for good when The Doobie Brothers were discovered by Warner Bros. A&R rep Ted Templeman.

The band developed the early sound with Templeman, who would nurture Van Halen with Doobies engineer Donn Landee, adding rustic touches of country and gospel influences on songs such as “Listen to the Music” and “Jesus Is Just Alright” from 1972’s Toulouse Street. Bassist Tiran Porter, an ex-bandmate of Simmons, brought his baritone to the mix and completed the classic vocal harmony sound of the Doobies’ early period.

Hits such as “China Grove” and “Black Water” led to phenomenal success, but Johnston was eventually sidelined by a stomach ulcer condition that had plagued him since high school. Enter Steely Dan studio musicians Jeff Baxter on guitar and Michael McDonald on keyboards and vocals, and a new direction largely characterized by McDonald’s blue-eyed soul sound. “Takin’ It to the Streets,” “What a Fool Believes” and “Minute by Minute” set the stage for soft rock, but Act 2 of the Doobies’ career ended in 1982, with Johnston joining the band for “China Grove” at their final concert.

By 1987, Johnston was healthy enough to rejoin the band, minus McDonald, and the Doobies have been back ever since. Simmons and McFee are master musicians, the harmonies are on point, and being able to catch Johnston and McDonald trading off lead vocals live in concert is a buzz any classic rock fan would want to catch.

Planet Hollywood Resort, 8 p.m. May 18, 20-21, 25 & 27-28, starting at $69 plus tax and fee. ticketmaster.com

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