"Don't go nowhere," Earth Wind & Fire lead singer Philip Bailey urged the jubilant crowd at the end of his group's terrific set Saturday night at Xcel Energy Center in St. Paul. "Don't go nowhere. Don't go nowhere."

That's because something special was about to happen. Chicago, the night's opening act on the Heart & Soul 2024 Tour, was set to join EWF for an extended encore that would culminate in a knockout version of "25 or 6 to 4."

You know "25 or 6 to 4," that song that every high school and college marching band has been playing for decades. Chicago has been performing it since 1970 when it became a hit off their second album. But not quite the way they played it Saturday.

Chicago's Tony Obrohta kicked it off with buzzsaw guitar as EWF's Verdine White added some funky bass before the Chicago three-man horn section stepped forward to deliver that familiar flourish. Neil Donell, Chicago's vocalist since 2018, offered his best impersonation of a soaring Peter Cetera. EWF's Bailey took the second verse, feathering it with his falsetto at just the right moment.

This nearly seven-minute reading of "25 or 6 to 4″ took on a slightly faster tempo and more surging intensity. Three guitarists — one from Chicago, two from EWF — traded solos midsong with EWF's Serg Dimitrijevic rocketing into outer space and bandmate Myron McKinley adding spikey filigree. Then the Chicago horns launched the tune into a new universe, echoing Donell's high-pitched tenor voice. Time for the bands to groove — all 23 musicians.

This horn-propelled rouser ended with EWF cofounder White, 72, and Chicago cofounding trombonist James Pankow, 76 — the most wired performers in their respective groups — front and center for a very physical and musical punctuation mark.

While that number may have been the climax of the encore, the preceding 25 minutes featured an exciting, seamless medley as the two Rock & Roll Hall of Fame bands alternated tunes, with all musicians on every selection. In the middle of Chicago's "Free" with its Latin percussion groove, a James Brown concert suddenly broke out with funky horns and EWF singer B. David Whitworth essaying fancy dance moves reminiscent of the Godfather of Soul.

The Heart & Soul Tour marked the first time these two groups — both started out in the Windy City in the 1960s — have toured together since 2018. Each played for 75 minutes before the encore. Despite having several radio hits in the '70s and '80s, these ensembles pride themselves on intricate, often jazzy musicality between singalong choruses.

Chicago did a nifty job turning a medley of "Make Me Smile" and "Colour My World" into an engrossing classical-tinged suite. The group gained momentum on "Beginnings," the best vocal by keyboardist and original member Robert Lamm, and "I'm a Man," which crescendoed with a drums-and-percussion duet.

As for Donell, the veteran Canadian studio singer, 68, hit those Cetera high notes, but his head voice sounded strained. Moreover, it seemed awkward for the ostensible lead singer to stand at the far right or far left of the stage, not in the center. And neither Donell nor Lamm bothered to introduce the 11 members of Chicago.

By contrast, EWF's set was undeniable. More energetic than last year's St. Paul show with Lionel Richie, the veteran R&B ensemble started with a bang, "Shining Star," got jazzy with the instrumental "Sun Goddess," slow jammed with the cuddly "Reasons" and "After the Love Has Gone," and then closed with a dance barrage of the falsetto-fueled "Fantasy," a funky remix of "Boogie Wonderland," the groovy "Let's Groove" and "September," which found a crowd of mostly baby boomers getting about as celebrative as they get these days.

Then Bailey, 73, implored the crowd not to leave. And all 12,000 fans stayed for the encore. He was right.

At the end of the fulfilling and exhausting 3½-hour program, Bailey piped up again: "I got one question to ask: Can you feel the love?"

That said, the six original members — three from each band — took a bow. And White and Pankow walked off together, an arm around each other.