Who was the first act to sell out the Minnesota State Fair grandstand in 2017?

Not any of the three Rock and Roll Hall of Famers. Not the biggest rock band to emerge in North America in this century. Not the country superstar with 20 No. 1 hits.

No, it was an act that hasn’t had a radio hit. It was a group that has scored two No. 1 albums, earned three Grammys and chalked up 2.6 billion views on YouTube. Pentatonix, that little ol’ a cappella group from Texas, drew 13,139 fans, who ranged in age from about 3 to at least 75.

PTX, as the group is known to fans, charmed the crowd with nifty vocals and visuals, well choreographed movements and a smartly paced 90-minute performance without instruments (save for Kevin Olusola’s alluring mashup of vocal beatboxing and Bach on cello).

There was even audience participation, with six fans joining PTX onstage. Three of them joyously sang along to “Misbehavin,’ ” one of the group’s originals, while the other three just moved to the music. One of them, 75-year-old Florene, received boos when she said she was from Wisconsin. That prompted one of the PTX singers to declare: “Mixed reviews.”

That might be an accurate assessment of Pentatonix’s performance because its original material, which dominated the beginning of the set, is neither strong nor memorable. Their own tunes tend to be intriguing vocal exercises rather than compelling songs likely to be interpreted by other singers.

When PTX did covers, things got exciting. Their Grammy-winning Daft Punk medley and quick hitting tour through Michael Jackson’s catalog were complex undertakings with big musical and emotional rewards.

The quintet tackled Queen’s “Bohemian Rhapsody” with aplomb, minimalism and drama. Before the song started, singer Scott Hoying pointed out that they were nervous about taking on this classic.

“Rhapsody” was not in PTX’s set list in October at Xcel Energy Center, though much of the material was the same at both shows. Two other smart additions were the Andrews Sisters’ peppy “Boogie Woogie Bugle Boy” and John Lennon’s “Imagine,” during which a video showed the five members, ages 25 to 28, holding signs of identity and diversity — LBGTQ, Jewish, Christian, Latina, black, American, ending with them holding letters that spelled H-U-M-A-N. It was a potent and timely message without being heavy handed.

Another timely message was delivered by popular bass singer Avi Kaplan, who is leaving PTX at the end of this tour (which has only three more shows). He thanked everyone for six great years since the group won “The Sing-Off” in 2011. Then, as the five singers gathered around a giant light bulb, he solemnly crooned “Light in the Hallway,” a benediction about knowing you are not alone.