One of the most eagerly anticipated moments of Taylor Swift’s concerts on The Eras Tour is the “surprise song” acoustic segment. It comes late in the show, between segments devoted to “The Tortured Poets Department” and “Midnights,” the final chapter.

Swift often brings out special guests to help sing the surprise songs. No guests joined her on Friday, Oct. 25, the first of the Eras Tour’s three nights at the Caesars Superdome in New Orleans.

But she pulled off a big surprise on Saturday.

“I think tonight I’m going to do something completely different,” she said at the outset of the acoustic segment. “I’m going to sing a song that’s not mine, but it’s somebody that I really love. So I want to see how loudly you can sing the song.

“It’s been stuck in my head. It would make me feel good if I knew that 65,000 other people had this song stuck in their head just like I do.”

With that, she started singing “Espresso,” by Sabrina Carpenter, one of her former opening acts who is now an arena headliner.

“I love my friend and I’m just so proud of Sabrina,” she said. “She was opening up on the Eras Tour earlier this year. This year she has absolutely taken off. Her tour, you can’t get tickets to it. The album is No. 1 constantly. I know she’d really love to know how loudly you just sang that song. Is it okay if I call her?”

She took out her cell phone, dialed Carpenter — who is currently headlining her own Short n’ Sweet Tour — and held the phone up to the microphone.

“Is there any chance you could get off the roller coaster you’re on and, like, put on some clothes, and just like come out and sing with me?” Swift asked. “How long would that take you?”

Carpenter replied, “It would take me like five seconds.”

With that, she rose up from below the stage in a short white babydoll dress, as the arena erupted in screams.

With Swift strumming an acoustic guitar, they joined together for “Espresso.”

“Can I do it?” Swift asked.

“You can do it,” Carpenter replied.

“Oh my God, I’m about to do it,” Swift said, then belted the infamous Carpenter line, “I’m working late, ’cause I’m a singer.”

They mashed-up “Espresso” with Carpenter’s “Please, Please, Please” and the Swift “1989”-era deep cut “Is It Over Now?” as fans screamed the lyrics from their seats.

After their “Espresso” mash-up, Carpenter strutted back down the stage runaway and disappeared.

Carpenter had performed her own show in Tampa on Friday, and is slated to play Houston’s Toyota Center on Sunday.

“She has literally one day off,” Swift said. “She is on tour. This is crazy that she came to perform for us.”

She added, “Fun Saturday night so far, huh?”

It got even more fun as Swift sat at the piano and mashed up “Hits Different,” a bonus track from “Midnights,” with “Welcome to New York,” from “1989 (Taylor’s Version).”

The remainder of the show featured the same songs from “Midnights” that typically conclude the Eras Tour.

Friday night surprise songs

On Friday, the first of Swift’s three sold-out nights at the Caesars Superdome in New Orleans, she went to her debut album for “Our Song,” which she coupled with “Call It What You Want,” from “Reputation,” in the acoustic guitar mash-up.

A piano mash-up of “The Black Dog,” from “Tortured Poets Department,” and “Haunted,” from 2010’s “Speak Now,” followed.

The previous weekend in Miami, Florence Welch of Florence + the Machine made a surprise appearance with Swift to sing “Florida!!!,” after previously appearing on the recorded version.

Nola.com reporters Chelsea Shannon and Lauren Walck contributed to this report.