ERIN, Wis. -- U.S. Opens are four-battle wars, and the winner is often the one who sheds the least amount of blood. As the casualties mount and the drama thickens, it's important to remember that there are innumerable ways to get to that podium on Sunday. Some of those four battles require defense, others require offense and some more a hybrid of the two.

On Thursday, Rickie Fowler charged out in front with a bogey-free 65 that doubled as one of the most impressive first rounds in tournament history. He was clearly on the offensive. 

One day later, it looked like more of the same as he went out in 34 and extended his bogey-free streak to 27 holes. Then came the second nine on Friday, and all of a sudden Fowler had to play defense. Bogey at holes 11-13 caught him off guard, and he willed himself to pars coming home.

"I hate just being in the situation where I've been in a good spot and maybe let it get away from me a little bit," said Fowler after dropping a 73 in the second round to finish at 6 under through 36 holes. 

"Let some mistakes compound and turn a round that you kind of fight through it and end up being in a decent spot after the day. I've been in positions where there's been a couple that have kind of gone the wrong way and you miss the cut. You look back, and I just grinded it out."

The result of his Friday grind? He lost only one stroke on the day and trails Brooks Koepka, Paul Casey, Tommy Fleetwood and Brian Harman by just one.

Fowler hit three fewer greens in regulation on Friday than he did on Thursday, and he made three more bogeys. That's not a coincidence. Getting up and down at any U.S. Open is difficult, and Fowler didn't make the monster putts he needed in Round 2.

Still, just as was the case on Thursday, there is a long way to go to the end of the war. Fowler got his bad day out of the way, and he has the most staying power of anybody in the top 12 on the leaderboard. He can settle in for an important Saturday to set up the denouement on Sunday.

"It's one of the hardest tests of golf that we get through the year," said Fowler. "It's our national championship, so to be in a good position to go play well this weekend and have a chance to win it, it's special. It's a special weekend."

In a week that lacks the gusto of previous Opens and major championships, Fowler is the clear-cut favorite in Las Vegas (5/1), with golf's governing bodies (he can reach millennials!) and among the patrons on the ground here at Erin Hills.

As Rickie strode home on No. 18 on Friday with a par finish, his short, quick gait was never out of tune with his blase face. Fowler's name emitted from the rolling farmlands and spewed into the dusty air. Children chanted at him, and their parents smiled. 

Fowler hasn't let himself break character just yet because, remember, this was just battle No. 2. But the deck has been cleared of stars and Fowler has already fought maybe his toughest fight. Yes, there will be trials, but his swing looks tight and he doesn't have to run down anybody he's incapable of running down. Fowler trails by the slimmest of margins going to the weekend with little standing in the way of him and his first grand prize.

The feeling in Erin, Wisconsin, is undeniable. This is Fowler's Open.

1. Stars miss the weekend: As I referenced above, only Fowler, Sergio Garcia, Jordan Spieth and Hideki Matsuyama made the weekend of those ranked in the top 10 in the world. Rory McIlroy and Jason Day were joined on the missed cut list by Dustin Johnson, Henrik Stenson, Justin Rose, Jon Rahm and Alex Noren. Incredibly, this is the first time the top three in the OWGR have ever missed a cut in the same major.

2. Paul Casey's birdie streak: Maybe the most impressive round of the day on Friday was Casey's 1-under 71. That doesn't sound all that impressive, right? But consider the fact that he started par-birdie-bogey-par-triple-bogey to drop all the way to 2 under, five back of Fowler at the time. Then he recovered by making birdie at five of his next six to get it back under par on the day. "I asked [my caddie] if he was all right because he was incredibly quiet (after the triple)," said Casey after his round. "And he was like, 'Oh, fine, I'm good.' He's like, 'Are you all right?' I said, 'Yeah.'"

That proved to be true as Casey he nearly set the 36-hole U.S. Open birdie/eagle record coming home. He'll have a great shot at his first major this weekend. "Not every day you enjoy a round of golf with an 8 on the card, but I'm a pretty happy man," said Casey. "Yeah, it was a bit of a roller coaster. If you can get through, I guess it's where you get through a U.S. Open or any major without some kind of hiccup."

3. Fowler's bogey streak: I mentioned it briefly above, but Fowler actually extended his bogey-free streak to 28, which is tied for the second-most ever behind Rory McIlroy's 35 at the 2011 U.S. Open at Congressional.

4. These scores! If you want some perspective on how easy this course has been this week (relative to other U.S. Opens), it's not even the most difficult first 36 holes in the last month of golf. The cut line of 1 over turned out to be three (!) shots easier than the Dean & DeLuca Invitational at Colonial. It should be noted, though, that Colonial plays to a par of 70 versus the par 72 we're seeing at Erin Hills.

5. Brooks is here: The name I'm most concerned about of everyone on the leaderboard if I'm Fowler is Koepka. He's hit 30 of 36 greens in regulation, and he's doing it the easy way because he's forever off the tee. "I've only hit 7-iron, that's the longest I've hit into any par-4," said Koepka. "When you're doing that, you've got to be able to put it on the green. Some guys are hitting 4-iron into the greens, and having a wedge and a 9-iron. I've got to put it close."

I don't know if Fleetwood, Casey and Harman can win this tournament. I know Koepka can.

6. Who is Xander Schauffele? If you flipped on the U.S. Open on Friday, saw the leaderboard and thought, "I know Rickie Fowler and I've heard of Paul Casey, but who in the world is Xander Schauffele?" then you're not alone. Schauffele is playing in his first major championship and is the No. 352 player in the world. He also just shot a 66-73 in his first two rounds at Erin Hills and sits T8 after two rounds.

In 17 starts in his first PGA Tour season, Schauffele has just one top 10 after narrowly getting his PGA Tour card following an above-average year on the Tour in 2016. He actually barely even got on the after turning pro as he sneaked in via Q-school by a single shot in December 2015. In short, he's a good player who has not yet found success at the highest level. The son of a German father and Tiawanese mother, Schauffele grew up in California where he won the California State Am in 2014 over Beau Hossler. He knows he's not the most popular guy in this field, but he's having some fun with his success after shooting 5 under over the first two days.

"It's funny, I'll sign some autographs and kids will be like, 'Dad, who is that?' That's just how it is," said Schauffele. "I remember when I was a kid and I didn't know the top five, one of the top five guys in the world wasn't trying to sign my hat, I was like, 'Hey, dad, who is that?' But, yeah. I'm sure. It's just two rounds of good golf, and hopefully Schauffele is a pretty weird name to remember."

7. We need to talk about Cameron Champ, don't we? Champ is leading the field in driving distance. I repeat, an amateur is leading a field with Dustin Johnson, Bubba Watson and Rory McIlroy in driving distance!

"It feels great," said the Texas A&M Aggie. "I came in this week with no expectations really at all. The only expectation I had was to be low am. I played well. In college I normally am the longest. Yeah, I guess I've just kind of always been that way. I don't talk about it much. You've still got to make a score. Here if you can hit it long and straight, it's a great advantage. I took advantage of it the last few days.

8. Two 65s: The two lowest rounds of the day go to Hideki Matsuyama and Chez Reavie. Matsuyama vaulted all the way to T8 and 5 under overall. He nearly caught Fowler after trailing by nine (!) to start the day. Those two 65s were the best round of any of the 156 players in the field by three strokes. Matsuyama was completely out of his mind. He went out in 30 and missed an easy birdie putt on No. 12 that would have put him on pace for a record-tying 62. I'm not sure he can sustain it throughout the weekend, but he could be a factor over the final 36.

9. Fowler still wins: I said on Thursday that I think Fowler wins this thing, and nothing that happened on Friday changed my mind. I think he shoots 72-71 on the weekend for his first major championship.