NOBODY in rock music has it harder than the opening act, just ask LCD Soundsystem, which warmed up the Jones Beach Theater for the reunited, rejuvenated Pixies on Tuesday.

Although the New York-based pop-dance quintet played to 14,500 empty seats and a mere 500 fans – who got to the seaside amphitheater early enough for a 7 p.m. set – they delivered a succinct, killer set.

With more humor than frustration, good-natured LCD frontman James Murphy joked with the audience: “We’ll be playing here every night, before anyone shows up, all summer long.”

Another hometown band, Interpol, filled the middle slot with a middling performance. Never a band that’s indulged in stage histrionics, the quintet did plenty of shoe-gazing, and singer/guitarist Paul Banks let the emotions and the performance of the songs dominate.

Interpol’s “music first” attitude made them seem detached and aloof during a set focused on their sophomore disc, “Antics.”

By the time headlining act the Pixies took the stage, the crowd had swelled to an unimpressive but devoted 8,000 fans, brought to ecstasy by the band’s dynamic quiet-verse, loud-chorus songs.

Bandleader Frank Black, 40 and fat, looked like an Uncle Fester impersonator, but his voice retained the same power it had during the Pixies’ glory days more than a dozen years ago.

That’s a major improvement over last December’s eight-show series at the Hammerstein, where after a 90-minute set, Black’s voice – and ultimately the performance – faltered. With half a year of touring under his considerable belt, Black’s edge, as well as the band’s, is now honed sharp.

Rather than looking lost onstage – as she did at the Hammerstein – bassist Kim Deal was all smiles and vivaciousness at Jones Beach. She and Black, known for their feuding ways in the bad old days, sounded great in the many duets that demanded boy-girl harmonies.

There were times when Deal’s mike should have been turned up, but on her star turn, the raunchy “Gigantic,” she sounded fine. Black made his mark with the throat shredder “Broken Face,” but the fans cheered loudest for the college-radio favorite “Where Is My Mind.”

Style-wise, LCD Soundsystem’s dance grooves, Interpol’s hipster emo and the Pixies’ post-punk rock delivered an eclectic musical mix. But the three bands shared a fondness for irreverent lyrics, as well as a devotion to the music despite empty seats.