"It feels good", said the 39-year-old, who has recorded three consecutive top-six finishes in the Masters but whose sole top-10 finish in 13 US Open appearances came at Oakmont a decade ago. It's just that you've got to keep it in the short grass, out of that fescue, don't make any bogies. But as a younger golfer, he didn't always enjoy that sort of pressure.
But the former Irish Open victor posted one under for the back nine to get into the clubhouse just inside the cut mark. With wind a nonfactor, a red-number logjam emerged on the first page of the leaderboard with two rounds to play in the second major of the season.
Tommy Fleetwood was relaxed about sharing the lead at the halfway stage of the US Open as the absence of some of golf's biggest names set up an intriguing weekend at Erin Hills.
Casey chopped his way to a triple bogey, only to respond with five straight birdies that carried him to a 1-under 71 and make him the first to post at 7-under 137.
The lead, however, belonged to Brian Harman.
"I was in the hay too much over the last couple of days", Day said. "Yeah, it was a bit of a roller coaster".
The historic round also took Thomas, a three-time victor on the PGA Tour this season, to 11-under for the championship and a two-shot lead over compatriot Brian Harman and Englishman Tommy Fleetwood, still on the course. Five players are at 5 under - Si Woo Kim (70), Xander Schauffele (73), amateur Cameron Champ (69), Brandt Snedeker (69) and Hideki Matsuyama, who tied for the low round of the day with a 7-under-par 65.
"Yeah, 12 under, I'd have about a 10-shot lead in most Opens", he said. The soft Black Course allowed players to take dead aim, and Barnes opened with rounds of 67 and 65.
Matsuyama, the world number four, had to settle for a one-under-par 71 which left him on six under, six off the pace.More news: Rivals 'all Team Scalise' as political baseball clash honours shot Republican
Both players liked the course but put their performance down to a lack of execution.
Shane Lowry is the only Irish golfer now inside the projected cut mark of 1-over at the US Open as Day 2 unfolds. Jordan Spieth was even par through 12 holes and going nowhere.
McIlroy won the US Open with a record 16-under-par total in 2011, but was a combined 50 over par for his seven other appearances before this week and missed the cut at Oakmont previous year following rounds of 77 and 71.
For the first time in a major, the top three players in the world all failed to make the cut. But I think at the end of the day it's competitive rounds with a card in my hand that I need and I've been very light on them this year.
"I couldn't have shot any higher", Johnson said. So it's pretty simple: I just didn't get it in the hole fast enough.
"I was upset with the score I had made, but it had, in no way, any effect on my attitude or how I was going to then approach the rest of the round or the next shot". If it is, it'll be quickly extinguished by the rain slated for the weekend.
"It was a good display, all my own fault, of what can happen if you get out of position on this golf course". If the storms stay away, Erin Hills could become a nasty beast.
"I think with everything so large, your target is larger and your misses get even more extreme".