Camila Cabello worked the TD Garden stage in a ruffled dress a shade of red hotter than Santa’s suit, but the real reason the 21-year-old Cuban pop singer practically stole the show at Tuesday’s Kiss 101 Jingle Ball went beyond her look. When she crooned an a cappella snatch of Elvis Presley’s “Can’t Stop Falling in Love” and moved to piano for the unadorned love song “Consequences,” Cabello dispensed with the backing vocal tracks that she shared with other performers at the annual radio show and showed she could really sing with style and substance. Then she went back to pop Latin-style to romp with dancers to “Havana,” leaving to a blizzard of red confetti that reached into the corners of the arena.

Cabello reportedly also hung out backstage with Shawn Mendes (let more rumors fly), the Toronto heartthrob who honestly bested her when it came to love from the young (granted, largely female) crowd, particularly in social media posts on the big screens. The casual Mendez carried himself well, despite the looming threat of being overshadowed by fan cheers. The singer built darker tension in “Mercy” (though his double-time clapping at mid-song went against the mood) and likewise leaned into sustained notes in his closing plea “Treat You Better.”

Shawn Mendes played Kiss 101 Jingle Ball on Dec. 4. 

The Chainsmokers’ Andrew Taggart and South Korean boy band Monsta X played Kiss 101 Jingle Ball on Dec. 4. 

Mendes and Cabello never joined forces to sing their joint song “I Know What You Did Last Summer” — maybe it’s the wrong season or they didn’t want to break hearts of the hopeful. For that matter, collaborations were scarce at Jingle Ball, even though many of the night’s acts had done features on each other’s records. The Chainsmokers, however, are kings of collaboration and frontman Andrew Taggart brought out South Korean boy band Monsta X to sing along to “Something Just Like This,” though the Chainsmokers’ real ace in the hole was monster drummer Matt McGuire, whose flailed crossover beats generated more heat than the pyro geysers. Local hero Meghan Trainor also acquitted herself well in a brief early slot, opening with her cheek hit “All About That Bass” and performing in a greenish black Santa outfit.

For their part, Monsta X closed out the three-plus-hour Jingle Ball (counting commercials and DJ breaks) with hypnotic choreography that took Michael Jackson’s Thriller-era ensemble style to a slick new level. Still, the K-pop septet hasn’t quite captured an audience here – or the majority of the crowd (dotted with fans sporting reindeer barrettes with blinking blue bows) simply hit curfew. After a typically sublime turn from singer Khalid, who seemed both heartfelt and nonchalant (at one point, bending over to tie his shoelace), the crowd filed out in droves, leaving Monsta X to go through their motions for a largely empty Garden. On that count, the group’s “Dramarama” fell short, although years from now, some pop fans might still claim to have been there.