Sorry, Jessie J. Looks your chair-ridden ubiquity throughout tonight’s show isn’t enough to have people Googling and Tweeting about you at every commercial break. California’s own Young the Giant gladly accepted the role of Underdog Rock Band, by delivering an energetic performance and representing for this year’s seriously depleted genre. The band was backed by fans from their hometown in Irvine, Calif., inside the theater’s strange tunnel stage, who jumped triumphantly thus giving the idea that if you don’t know these guys yet, you should. Frontman Sameer Gadhia switched off between stroking two microphones and managed to create an effortlessly fun and sensual vibe to “My Body.” Give the man some cool points for stage diving, not once, but twice.