Judge Randy Jackson had said on Tuesday's program that Glocksen — the show's resident rocker girl, with her red highlights and all-black outfits — gave a "nice, controlled performance" of the classic song "Smile."
His colleague Simon Cowell, who has griped that Glocksen was not in the same league as other finalists, sported a frown.
Glocksen let out a sob when she heard the result but managed to sing through her tears while performing on "Idol" for the last time.
Haley Scarnato and Phil Stacey had the next-lowest vote tallies in the phone balloting, which drew about 33 million calls and text messages.
Scarnato, 24, of San Antonio, is not opposed to showing a little skin on "Idol." Though Cowell derided her take on "Ain't Misbehavin'" as a bit "pageant-y," he applauded her "nice legs."
Cowell said Stacey's performance of "Night and Day" was too dark and dreary, while— this week's venerable guest coach — heaped praise on the 29-year-old Floridian, calling him one of the best singers he's heard.
Wednesday's program also featured a performance by Michael Buble, who sang "Call Me Irresponsible."
Among this week's survivors were favorites Melinda Doolittle, LaKisha Jones and Jordin Sparks. Sanjaya Malakar — the stringbean teen who's anything but a judges' favorite but still manages to rack up viewer votes — also made it through.
In its sixth season, "American Idol" continues to rule the ratings. It has attracted 26 million to 37 million viewers per telecast this season.