You don't expect to hear classic rock 'n' roll and old-school funk during the same concert, much less on the same stage. But then again, you generally don't feature bands as versatile as Chicago and Earth, Wind & Fire, and they made it work Wednesday night.

The reason the Post-Gazette Pavilion concert did work was simple: The guys in both bands are first and foremost musicians, ready, willing and able to play any kind of music. It's not simply what they do; it's who they are.

Not only that, but the groups actually have many similarities. Both hail from the Windy City, employ horn sections, feature numerous lead singers, maintain tight vocal harmonies and borrow heavily from jazz. And if the concert was any indication, they do enjoy playing together.

The mutual admiration show started off the bat as members from both bands came out together with "Beginnings," "In the Stone" and "Dialogue," then playfully flipped a coin to determine which of them would go on first -- this night it was Earth, Wind & Fire.

Not surprisingly, this did become a greatest hits show, EWF opening with "Boogie Wonderland" and sliding into a Broadway dance routine on "Getaway."

Philip Bailey, he of the legendary falsetto, led its smoother-than-usual rendition of the Beatles' "Got to Get You Into My Life" -- Chicago also has done it, but only live -- and the EWF classic "Reasons," though the folks who might have expected the usual call-and-response between Bailey and saxophonist Gary Bias were disappointed.

A nice surprise was the closing "Mighty Mighty," one of the band's very first hits that even preceded the assembling of the Phenix Horns.

Stealing the show at times was Russian-born lead guitarist Vadim Zilberstein, who ripped through "That's the Way of the World." I heard a few people asking, "Who is this guy?"

Opening its set with "Ballet for a Girl in Buchannon," the suite that includes "Make Me Smile" and "Colour My World," Chicago's performance, on the other hand, was more staid and, by its standards, a bit uneven. I don't fault the band, however.

For openers, I don't mind if a guitarist turns it up loud from time to time -- Chicago is, after all, a rock band -- but Keith Howland simply drowned out everybody else on "Alive Again" and "Old Days."

"If You Leave Me Now" featured Bailey on lead vocal and Zilberstein sitting in on acoustic guitar, but a harmonizing Jason Scheff, who normally does the vocal, quite literally couldn't be heard.

This was definitely more a Chicago crowd, which came to life during "Saturday in the Park," pianist and lead vocalist Bobby Lamm bopping about the stage with a portable keyboard, and it stayed on its feet during "Feelin' Stronger Every Day."

But it was when both bands played together that their musicianship really showed. On the last set, Chicago bassist Scheff and organist Bill Champlin made EWF's "September" their own, and EWF bassist Verdine White, never lacking in the energy department, grabbed a tambourine during "Does Anybody Really Know What Time It Is?" and played it against his foot.

"Free" simply blasted, with the six horns nimbly navigating the interlude; White planted a kiss on the forehead of Chicago saxophonist Walt Parazaider before he and Bias began trading off, White facing the guy who was playing at the time.

You know Chicago won't get out of a show alive without doing "25 or 6 to 4," which led to another battle royal with Howland, Zilberstein and EWF rhythm guitarist Greg Moore each letting it all hang out.

And right before Chicago's set, Chicago drummer Tris Imboden and three EWF percussionists hooked up for a crowd-pleasing "groove summit" of sorts.

The only thing that seemed to be missing from Wednesday's show, aside from favorite songs there simply wasn't room for, was EWF founder Maurice White, who had to retire several years ago due to Parkinson's disease.