The flu-stricken Sara Evans downed medicine and whiskey before Friday’s show, but you (hardly) would have known. (Russ Harrington)

What do you get when a strep-throat-stricken country singer takes a mix of antibiotics and flu medication, and washes it down with a shot of whiskey before taking the stage?

Turns out, it’s an extra-candid Sara Evans, who headlined a sold-out concert at the Fillmore Silver Spring on Friday night for the WMZQ Christmas Show. Evans, suffering from strep and the flu, said she nearly had to cancel her appearance, but didn’t want to bail when she already dropped out of a Fillmore show earlier this year due to illness.

“I am feeling so good,” Evans drawled, happily ticking off the long list of medicine she had taken that day. Then, she tried to give a shout-out to her opening act: “Blake Shelton rocks!”

Maybe true, except Blake Shelton was not one of her openers. Evans paused. “Oh wait,” she said slowly, realizing she had confused which male country singer had been on stage minutes before. “That was Joe Nichols.”

Looking mortified as her guitar players cracked up and the audience cheered, Evans tried to compensate: “Blake Shelton rocks, but Joe Nichols rocks harder.”

Evans covered her face with her hands. “I’m just going to shut up and sing — ’cause I think I’m high as a kite,” she joked.

Without her introduction, you never would have known Evans was ill. Though her speaking voice sounded slightly hoarse, her crystal-clear powerhouse twang was as strong as ever over the acoustic set. With a performance cut to just 30 minutes and six songs, she stuck to her best-known material, including up-tempo hits “Born to Fly,” “A Real Fine Place to Start” and “Suds in the Bucket.”

She also played “A Little Bit Stronger,” her comeback smash in 2010 after taking a career hiatus. Evans dedicated the powerful song about overcoming a tragic situation to “everyone who lost a precious loved one in Connecticut today.”

Evans’s near-cancellation explained the sudden presence of Nichols, announced as a “surprise guest” mere hours before the concert. Nichols, brought on stage to fill some time and banter with the crowd, said he got the call to play at 10 a.m. in the middle of a haircut. Negotiating with someone off stage for more time, the country crooner squeezed in his most popular tunes, such as “Brokenheartsville” and “Size Matters.”

Opening act Edens Edge, the dynamic trio from Arkansas led by Hannah Blaylock, provided the most somber moment of the night, closing out their set with an a cappella version of “Christ Alone,” which they dedicated to the victims of the horrific elementary school shooting in Newtown, Conn., earlier that day.