“My career is going to college,” Carrie Underwood quipped early on in her Sept. 3 concert before 6,852 fans at the Great Allentown Fair.

Underwood was referring to her 17-year career, dating to her winning “American Idol” in 2005.

In her third appearance as headliner at the Fair’s Grandstand, Underwood put on a phenomenal concert that demonstrated that her years of career “classes” as songwriter and touring concert performer has prepared her well for “college.”

The 8:15 p.m. start of Underwood’s Fair Grandstand concert rang out with “Church Bells,” followed in quick succession by “Southbound” and “Cowboy Casanova.”

“It’s great to be back. This isn’t my first time here,” she said. Underwood headlined Fair Grandstand concerts in 2007 and 2015 at the Allentown Fair.

Underwood puts her whole body into her performances, leaning forward, crouching, knees bent to belt out the big notes. Her animated style was emphasized by a flashy outfit of black knee-high heeled boots, black sequined shorts and top.

The big notes were frequent and impressive. Her voice is a magnificent instrument that is as powerful as it is subtle. She’s able to navigate the crescendos and the quiet moments of her hit songs, many of which she’s written.

She’s not afraid or embarrassed to give credit to where she feels credit is due. “The good Lord has done some awesome things,” she said. Recalling seeing Alan Jackson and Faith Hill concerts as a fan, she said, “I didn’t know how I’d get on the stage.”

On stage, she’s not only a forceful performer, but a comfortable performer.

When she walked up the stage riser steps center stage to perform “Choctaw County Affair,” and found that there was no harmonica there, she matter-of-factly said, “I’m about to perform the harmonica.” But there was no harmonica. “No pressure,” she joked.

A harmonica was soon brought, and Underwood proceeded to do a harmonica duo and solo bar none.

Speaking of bars, the big screen in the center of the stage provided the image of a saloon exterior for “Drinking Alone,” which included a tremendous saxophone solo.