One of the biggest turning points in Kelley O’Connor’s career also happened to be a notable moment for the Chicago Symphony Orchestra.

In May 2008, the mezzo-soprano made her second-ever CSO appearance for her debut performances of Peter Lieberson’s Neruda Songs, settings of works by 20th-century Chilean poet and diplomat Pablo Neruda (1904-1973). Lieberson wrote them in 2005 as love songs for his wife, mezzo-soprano Lorraine Hunt Lieberson.

But the famed singer performed them only a few times before dying the following year of cancer. Lieberson turned to O’Connor, who was just 28 at the time, to take his wife’s place, teaching the songs to her in March 2008 — one a day — and explaining what they meant to him.

“Once it became that personal to me that he became a friend to me, I felt honored to tell their story, because it is their story,” O’Connor told the Denver Post in 2008. “Every time I sing it, I feel as if she is saying it through me to him. I think it is just such a powerful message.”

The mezzo-soprano performed Neruda Songs first in Chicago with conductor Bernard Haitink and then traveled with the CSO to New York City for her Carnegie Hall debut — one of the highlights of her career.

In New York magazine, music critic Justin Davidson devoted a full page to the concert’s review, while acknowledging that he couldn’t put Lieberson’s recording of the songs out of his mind. He kept thinking there was something wrong with what O’Connor was doing. “It isn’t, though,” Davidson wrote. “Her interpretation will probably sharpen over time, mixing some muscular joy in with the sad softness, but she has visceral glimmer, excellent Spanish and technique and tone to draw out the songs’ surreal languor.”

Neruda Songs have gone on to become a pillar of O’Connor’s career. She has sung them with more than 20 orchestras, and she will add more ensembles to the list this season. In November, she will perform the song cycle with the St. Louis Symphony and then the Colorado Symphony in February.

“It also says so much about the writing,” she said of the work. “People just love the story of it. They love the melodies, and that it is so accessible.”