A profoundly beautiful late-August evening. One of the finest improvisation-based rock bands of all time. An opener who could have headlined the place. It all added up to make Friday night at Darien Lake one of the highlights of the summer concert season.

Why do people flock every summer to see the Allman Brothers at Darien Lake? Simple. You always know what you’re going to get. The Allmans’ default position is still a stunning show. Happily, that was not going to be a problem this time. This was not a “default” show. This was, then, real deal.

What we got Friday was a prime AB Band show. Everyone on stage seemed eager to prove something, and everyone played an admittedly hits-heavy set as if these songs were brand new to them. The group – pater familias Gregg Allman on vocals and keys, guitarists Derek Trucks and Warren Haynes, drummers Jaimoe and Butch Trucks, bassist Oteil Burbridge and percussionist Marc Quinones – delivered a soul-drenched set that ran continuously from 8:30 p.m. forward.

Opening with a low-key, groove-centered take on “Statesboro Blues,” the Brothers went on to offer standards, unexpected new tunes and some covers that entered the area of the sublime. When Haynes led the group into Van Morrison’s epic “Into the Mystic,” and the slightly more than three-quarters-full house flipped out in kind, we knew we were onto something. This particular number found Trucks and Haynes trading solos as they did throughout most of the evening. Rather than “cutting heads,” however, Trucks and Haynes urged each other on toward a common ground between their widely divergent styles.

Early on, a tour through “Don’t Keep Me Wondering,” “Midnight Rider” and “Hot ’lanta” yielded positive results. Trucks spent the early part of his set minus his trademark bottleneck slide, playing yearning-infused finger-style solos, while Haynes responded with deep, throaty Les Paul licks. The combined effect was mesmerizing.

“We got a good bunch here tonight,” Allman murmured to the crowd a few songs in, and yes, this was indeed the truth. The crowd eagerly followed wherever the band went Friday – toward a late-set “In Memory of Elizabeth Reed,” a midset eloquent run through “Desdemona,” which Allman killed, vocally speaking, or squeezing out another blues bacchanal in the form of “One Way Out.”

This band remains one of the finest of all the ensembles (perhaps unfortunately) lumped beneath the “jam band” tag. Blues, funk, R&B and country all appeared in their legitimate forms during Friday’s set.

Having Steve Winwood and his band open felt like an added bonus. Winwood centered his set on his work fronting Traffic, Blind Faith and the Spencer Davis Group.

Since Winwood-written tunes from all three of those bands have been part of the jam band catalog for decades, it felt appropriate that the man himself would open for one of the greatest jam bands extant.

Winwood’s set threatened to upstage the Allmans’ set at every turn. The man’s voice, first revealed to the public when he was but a wee 17-year-old with “Gimme Some Lovin’,” was in incredible form throughout his 50-minute set.

Winwood embraced Blind Faith’s “Can’t Find My Way Home” and “Had to Cry Today” early on. He emerged from behind his Hammond B3 organ to grab a Fender Stratocaster at various times throughout the evening and proved himself to be an incisive blues-based guitarist.

Of course, he proved the same 40 years ago. But there were clearly folks among the crowd who weren’t even born when Winwood had his second coming in the mid-1980s.

So Winwood seemed eager to prove something to listeners who might only know him for his pop hits like “Higher Love.”

By the time Winwood and his band had earned their fifth standing ovation, it was apparent that anyone unfamiliar with his contribution to what we now understand as “jam band” music had a pretty good idea of the man’s importance. What a voice, even after all this time.