Thomas has become just the 29th player to card 63 in a major; nobody has signed for lower. The Open always has been defined by its length, narrow fairways, hard rough and fast greens. In fact, it's wide-open going into the final round.
Day never had a chance, following his career-worst 79 in a U.S. Open with a 75.
Thomas established an Open championship mark by shooting 9-under 63, which broke Johnny Miller's record for lowest score in relation to par.
"I was a little mad at myself because I could feel I was hungry on 14 (where he parred the par-five) and 15".
The traditional moving day lived up to its reputation with a number of players exploiting benign conditions to tear into the forgiving par-72 layout.
It is almost impossible to predict because the competitors and their body of work offer no clear pattern.
Right behind was a trio of players that included Rickie Fowler, who went 28 holes before making his first bogey and then went three holes without making a par.
It was, however, enough to get him into the final pairing of a major championship that remains wide open. I've been there a handful of times and had some good finishes.
When asked, Harman said that he plays with a proverbial chip on his shoulder. He won the 2003 U.S. Junior Amateur and was also a member of the 2005 and 2009 Walker Cup winning teams. "Obviously it means I'll have to shoot 65 or 66 tomorrow to make the cut", he replied. I was trying to land the ball past the pin and draw it back.
Brian Harman 12 under; Justin Thomas 12 under; Tommy Fleetwood 11 under; Brooks Koepka 11 under; Ricki Fowler 10 under. Only a half-dozen of them have even experienced Sunday contention in golf's biggest events. And with no previous major champion within shouting distance of the lead (none within eight shots), Thomas has a golden opportunity to win his first.
Erin Hills' architects designed the course for the possibility of a back-nine sprint. So far, there have been 49 rounds in the 60s.
The par-4 15th was set up at 288 yards on Saturday, which explains why it played to almost a half-stroke under par, with three players making eagle.
"I'm not sure when it's going to sink in or when I'm going to realize what I did", Thomas said. "I think we'll be able to sit back, relax".
Yet this golf course is no snap. The venues typically produce a level of grumbling that has not been heard this week. He ends his weekend at Erin Hills at 1 over.
The wind at Erin Hills is finally expected to pick up for Sunday's final round, which could put a halt to all the record-setting scoring that's made the U.S. Open leaderboard look more like one at a regular PGA Tour stop.
But the bottom line is there will still be enormous pressure on Sunday. "It's interesting to see where the USGA has gone with the U.S. Open, being a little more friendly than in years past". This promises to be different, a shootout perhaps, but no less stressful.
"If someone shoots 9-under tomorrow in the top few (players), then I will have to shoot 10-under, I guess", Fleetwood said.