John Legend

Citi presents exclusive John Legend concert for Citi ThankYou Cardmembers at The Emerson Theatre benefitting Teach for America on April 21, 2014 in Los Angeles, California.

Charley Gallay/Getty Images for MAC Presents

As John Legend scores his first No. 1 on the Billboard Hot 100 and Hot R&B/Hip-Hop Songs with "All of Me," the piano ballad likewise becomes his first leader on the Adult Top 40 chart, where it rises 2-1. Notably, it's the first R&B ballad to rule Adult Top 40 since Mariah Carey and Boyz II Men's "One Sweet Day" (a fellow Columbia Records release) more than 18 years ago.

What's brought an unhurried R&B song back to the summit at a format historically known for its pop/rock lean? (Maroon 5, Katy Perry and P!nk share the mark for the most Adult Top 40 No. 1s, with eight apiece. Nickelback follows with five.)

"The track has a singer-songwriter feel to it," says Matt Sparker, music director at Adult Top 40 reporter KQKQ Omaha, Neb. "Yes, ['All of Me'] is R&B, but our audience doesn't shy away from slow, piano-driven songs. It isn't too far away from what they already like, but still different enough to stand out."

"I think it comes down to a song-by-song basis every time, and this particular song is just that special," says KLLC San Francisco MD Jayn. "It doesn't matter what format John Legend was previously known for."

Helping aid Legend's coronation is a recent invasion of R&B-flavored hits at the format from the likes of Justin Timberlake and, via multiple smashes, Pharrell Williams. (Some stations are also playing an uptempo Tiesto remix of "All of Me.") "The music cycle we're in allows this," theorizes KHMX Houston program director Bob Neumann. "There's the Pharrell factor, which can't be denied. ['All of Me'] fits like a glove. And, it's just a great song."

Pete Cosenza, Columbia Records senior vp of promotion, adult formats, says that he had high hopes for "All of Me" at adult top 40 radio despite the format's trademark inclination for tempo and guitars. The song's quality, however, reassured him of its potential. "The first time I heard it was last summer when John came to the Columbia offices and played his new album for us. When 'All of Me' played, I knew it was a very special song. The lyrics were amazing. I believed, from that very first listen, that it would immediately resonate with women."

KLLC was the first Adult Top 40 panelist to play the song, on Oct. 12, 2013, according to Nielsen BDS. Within days, WTSS Buffalo, N.Y., and KLTG Corpus Christi, Texas, were also spinning it, with the latter station the leader in plays to-date (nearly 1,500). "Others started jumping on board and we went into Christmas knowing we had something incredibly special and powerful," Cosenza says. "We came out of the holidays with momentum and, three weeks later, John had his amazing performance of the song on the Grammy Awards.

"The rest is history."

While "All of Me" has ruled two other radio charts, Adult R&B (for seven weeks in February/March) and Mainstream Top 40 (for three weeks running), its ascent to the Adult Top 40 summit was less widely envisioned. "I'll admit I was skeptical at first about the song," says WVMX Columbus, Ohio, assistant PD/MD Joe Kelly. "Slower songs can often struggle in a format where energy is tops. But, there is an amazing energy to this song that comes from emotional lyrics that connect."

Kelly echoes that the adult top 40 format has accepted more rhythmic hits of late. I.e., the title of Robin Thicke's "Blurred Lines," which topped Adult Top 40 for six weeks last year, serves as a metaphor for the mix of genres that the format's programmers now find more acceptable. "As with any pop-driven format, you have to be in tune with listeners' expectations. So, when those expectations grow and change, so must we. What was expected and accepted a year ago is different than today.

"I'm hoping that polkas don't become the next genre to pop …"

"'All of Me' is simply a beautiful song and performed with grace," says WVMX operations manager Jimmy Steele.

"When I hear it, I think about my wife, not how R&B it sounds."