Eight of the last nine occasions that Spieth has held the lead on the PGA Tour, he has gone on to win.
They'll take one of golf's most famous walks together again Sunday, and one of them may be celebrating his impending coronation as the Champion Golfer of the Year, the title bestowed upon the victor of this tournament.
"It's really a dream come true", he said after signing his card.
"That would be incredible", Spieth said.
Spieth has failed to keep his composure in the final round of a major before―fans won't need to be reminded of the 2016 Masters―but the course at Royal Birkdale hasn't proved challenging to the point something like that could happen on Sunday.
That over par round stood out even more on a day when Branden Grace became the first man in history to shoot 62 at a Major. He broke the previous mark of 63 by making eight birdies against no bogeys, finishing with a par from just off the back of the green on the 18th hole. Because Spieth has a wonderful chance to be a truly historic player who is clearly built for the toughest tests.
A birdie on the 17th saw Kuchar close the gap and he looked set to make another on the last, only to miss from six feet after Spieth had holed from more than twice the distance. He even briefly managed to tie Spieth for the lead when he birdied the 15th, but Spieth followed him in.
U.S. Open champion Brooks Koepka was six shots back, tied with Canadian Austin Connelly.
However, this championship has belonged so far to Spieth and, with the bit clearly between his teeth, it would be a major surprise if he doesn't go on to claim a third victory of the season after arriving on the Lancashire coast with victories in the AT&T National Pro-Am and Travelers Championship under his belt. This one left him nine shots behind. "If you keep it in play, it's nearly hard to make a bogey out there, you know?" I was there. But this thing is over.
Ian Poulter exploded into life on the first day and had placed himself right among it with an overnight score of three-under. The enormity of the moment, as he walked between The Open's large blue bleachers packed with fans and its trademark yellow scoreboards, caused Spieth to cease his usual pre-shot routine, though. He matched Kuchar's birdie on the third hole to stay one shot ahead. Spieth's 60-footer for eagle had raced by the cup, leaving a tricky putt with the hole cut on a crown. Kuchar dropped three behind after that double-bogey on 16, where he drove into a fairway bunker and three-putted.
"But, as long as I approach it positively and recognise this is the position you want to be in, then the easier it is to hit solid shots and to create solid rounds".
Kuchar's one-over-par round of 71, in the gusty winds Friday, was only slightly soured by a bogey on the 18th. I've believed when I turned professional that I was going to rise and be able to play with the best in the world. "Certainly, I'm not out of it". If I don't win tomorrow, it has nothing to do with that - it has to do with it was someone else's day, and I didn't play as well as I should have.
That's good news for Spieth and Kuchar, who are scheduled to tee off in the final twosome at 2:30 p.m. local time. But the Floridian has never played in the final group in a major.
Spieth has a chance to join Jack Nicklaus as the only players to capture three different majors at age 23. One small lapse, but one that can be costly for a player who has earned almost $40 million yet has never won a major.