Know what could be concluded from a zig-zag Friday at the Ryder Cup? Nothing.

For the U.S., there was a remarkable, take-that-history morning that no one could have realistically imagined, or barely dreamed about. A 4-0 sweep in foursomes. “Confidence breeds momentum,” Zach Johnson said. “I think that’s just what we witnessed.”

For Europe, an afternoon rally, answering a slow start with resolve – and a whole bunch of birdies – before it could turn into a crisis. A 3-1 win in four-ball. “They showed tremendous bravery, heart and desire,” captain Darren Clarke said.

So here’s the glass. Is it half full for the U.S., with a 5-3 lead after opening day? Had that score been offered to Davis Love III Wednesday night, he would have reached for it as if it were a gold bar.

But . . . you go up 4-0, you get greedy. “It was a long day, frustrating a little bit not to come out a little but further ahead,” Love said. “I know Darren is happy with the momentum.”

Or is it half full for Europe, having sent a message of resilience Friday afternoon, as “USA! USA!” gave way to “Ole, ole, ole, ole?” Right down to the final stroke of the day, an eagle putt by Rory McIlroy that was one big exclamation point on the second session. “We’re still behind on the cards in boxing terms,” McIlroy said. “We’re not going down without a fight. It was 4-zip after the morning. We’ve pulled it back a good bit and we play to pull it back even further going into tomorrow.

“Honestly, I think we’re going into the dressing room and overnight feeling a lit bit better than they are.”

But . . . as American Ryan Moore said, “A lead is a lead. That’s where you want to be.” And momentum Friday at Hazeltine was fickle. Here in the morning, gone in the afternoon. Or the other way around.

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Bottom line: This thing looks every bit as unruly and chaotic as Ryder Cups are supposed to be. “That’s the Ryder Cup,” Clarke said. “That’s what all these people come to watch.”

Actually, both sides took turns dominating the other. The PGA could almost have used Nos. 17 and 18 at Hazeltine for extra parking Friday. Only one match lasted that long.

It was a long, swaying day. The drama began before dawn, on a foggy, see-your-breath Minnesota morning.

By 6:23 a.m., the crowds were lining up, and the gang in red, white and blue Viking hats were already in section 103 by the No. 1 tee, chanting “USA, USA.”

By 6:25 a.m., with only floodlights to illuminate the practice green, Jordan Spieth took his first putt in the dark. Partner Patrick Reed had already come and gone. Early birds hoping for early birdies.

By 6:35 a.m., the stands by No. 1 tee were already filling. Somewhere unseen out there in the darkness and fog, the golf course was a rumor. But the merchandise tent was already open, if you wanted to buy shirts before breakfast.

At 7 a.m., someone carefully propped up a golf big on the left side of the tee box at No. 1. Arnold Palmer’s Ryder Cup bag from 1975 would stand by itself all morning. The crowd changed chants. “USA!” gave way to “Arnold Palmer!”

At 7:10 a.m. Clarke entered and waved to the gallery, including the fans wearing Darren Clarke masks. The guys in horns were singing “God Bless America,” which came after “Row, row, row your boat.”

At 7:30 a.m. the mighty applause was for Reed, walking onto the tee. Then Spieth, then Justin Rose and Henrik Stenson. The first foursomes group in the Ryder Cup featured four of the top 11 ranked golfers in the world. It was still not easy to spot the green up ahead, but what you could see were throngs of people, squeezing into any open spaces along the fairway. Signs of the enormous crowd to come.

And then there was quiet. Rose drove into the morning mist and fog, Reed followed, playing in shirt sleeves with temperatures in the low 50s. The Ryder Cup was underway.

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About 4 1/2 hours later, the sky was blue, and American golf was savoring its first opening session sweep since 1975 -- the same year Palmer used that bag standing at No. 1 tee. Some of this stuff, nobody could make up.

The U.S. camp had talked of needing a fast start, to blunt the echoes of the recent frustrating past. What it got was like the dropping the green flag at Indy. A 4-0 blur that came with constant, relentless, ever-growing noise from beyond the ropes.

Shadowed by their notorious losing streak, the American team understood what was at stake, “I played a little bit tight,” said Phil Mickelson, and he has been in 11 of these. But he had put himself in the bullseye with critical comments of Ryder Cups past, making himself the poster face for change. “The pressure was certainly as great or greater than I’ve ever felt. I could have copped out and asked to sit; that would have been a total weak move.”

Plus, he would have missed a great morning to be an American Ryder Cup golfer.

There was Rose, trying to explain how he and Stenson – the worst nightmare for the U.S. in 2014 – fell behind Spieth and Reed for good on the second hole. “They made a few putts. We couldn’t buy one.”

Or Sergio Garcia, describing a landscape of roars, coming when either a European missed a put or an American made one: “Massive crowds. Obviously, they are very excited. They should be. It’s our job to hopefully quiet them down.”

They did.

As the Europeans’ game heated in the afternoon sun – Stenson and Rose’s seven-birdie binge against Spieth and Reed in an afternoon rematch leading the way -- Hazeltine went from mayhem to murmurs. “They seemed to birdie every hole,” Love said.

“The response to this morning has been fantastic by the boys,” Rose said. “We’re a team that stands shoulder to shoulder.”

Among other things, Europe trotted out what, historically, has been one of its most fearsome weapons. Two guys from Spain. Once, it was Seve Ballesteros and Jose Maria Olazabal. Friday, it was Garcia and Rafa Cabrera-Bello; the Ryder Cup vet with 19 wins, and the surfer dude rookie, who birdied the first Ryder Cup hole of his life.

In the end, it all seemed a perfect lead-in for weekend, boisterous and turbulent. McIlroy punctuated his eagle with a sarcastic bow to the crowd, and said latter he was thinking about doing that before he ever made the putt. “It’s one I’ll continue to do because it’s a hostile environment out here and I want them to know how much it means to us; and sort of silence them like that.

“Obviously (we’re) not fazed by anything that is said by the crowd and not faced by anything that the U.S. team throws at us.”

And this is just the first day.

But then, the Ryder Cup is best when it is like a stormy wind, constantly changing directions without warning, pain and exultation in constant transition. And noisy. This is going to be good.