In short, it was one of the more boring Saturdays in the game’s oldest major, but, at the same time, that has helped set up a fascinating final circuit at the Sandwich venue in the last major of the season.
What looked at one point as though it could have become just a two-horse race as Oosthuizen, the 2010 winner, and Spieth, the champion in 2017, had moved to 13-under and 12-under respectively after 10 holes is not exactly wide open, but other title hopefuls are now lurking.
Canadian Corey Conners and Spieth’s fellow Texan, Scottie Scheffler, are both on eight-under, one ahead of US Open champion Jon Rahm, as well as Oosthuizen’s fellow South African, Dylan Frittelli, and another Canadian, Mackenzie Hughes.
Taking into account the fact that 94 per cent of Open champions since 1900 were either leading or within four of the lead heading into the final day, it’s going to be a battle between just five players.
But the likes of defending champion Shane Lowry and Scottish No 1 Bob MacIntyre, who carded the best round of the day with five-under 65 that included a 60-foot birdie to finish, will be among those bidding to be in the small minority upsetting the odds as they set out on five and four-under respectively.
On a perfect links day on the Kent coast, Oosthuizen looked to be free-wheeling as he birdied the seventh and ninth to be out in 33. But, out of nowhere almost, he then dropped shots at 11th and 13th.
He was unable to birdie the 14th, the easiest hole on the course, following a “horrible” swing with a 4-iron before steadying the ship by holing a 10-footer for par at the 15th then knocking in a birdie putt from a similar range at the par-3 16th.
“With a good back nine, I could probably have gone to 14 or 15, but that’s what this golf course can do to you,” admitted the leader. “There were a few very tough pins out there that you can't really go for at all while I also made a few bad swings.”
The Mossel Bay man has finished runner-up in the last two majors and six in total since getting his hands on the Claret Jug at St Andrews 11 years ago.
“Go one better,” he said of what he aimed to take from that run of near misses in the game’s biggest events. “You know, finishing second isn't great, so I will play my heart out tomorrow and see if I can lift the Claret Jug again.”
Does he feel the golfing gods owe him something on Sunday? “No. No, no. It's just golf,” he replied.
Morikawa, who is bidding to emulate 2003 winner and fellow American Ben Curtis by making a winning debut in the event at this venue, had been backpedalling as he dropped shots at the second and fifth.
Having admitted that he’d benefitted hugely from a Scottish Open warm up last week, however, the 2020 US PGA champion hauled himself back into the mix with birdies at the seventh, eighth, 13th and 14th.
“I think just believing in myself,” said the Californian in reply to being asked what had been the key in maintaining his composure. “I wasn't hitting that poor of golf shots. Just wasn't turning out great.
“No matter what happens tomorrow I know I produced good golf shots already this week and I'm capable of it. I just have to stick to that and believe in the process. Hopefully we can just put it together from hole one all the way through hole 18.
“It's going to be a gruelling 18, but I look forward to it. It's position you want to be in. As an athlete, golfer, you want to be in this position. I love it, so I really look forward to tomorrow.”
Of the trio at the top of the leaderboard, Morikawa has the most recent experience of getting the job done in a major. “I think I can draw from the PGA,” he added of that success at Harding Park last year.
“But I think confidence just comes from hitting good shots, quality shots, seeing putts go in. There is a lot to draw from, especially this week. I don't have much experience on links golf, and pretty much all the highlights in my head are from this week.”
Spieth carded five birdies and four bogeys, including two to finish after three-putting on each occasion, as he signed for a 69. It was a sign of his mood after that sign off that he headed straight to the putting green without offering any comment on his day’s work.
Rahm was three back when he won the US Open at Torrey Pines last month Helped by picking up three birdies in the last seven holes, giving him a 68, the Spaniard has set up a chance to become the first player since Tiger Woods in 2000 to win the US Open and The Open back-to-back.
“Really good round. Played good golf. Had some really good highlights,” said Rahm of his effort. “Because of the weather conditions, it's easy to think it could have been a little bit better, but the pin locations were no joke.
“I don't know if on TV you could appreciate it, but those are some of hardest pin locations collectively I've ever seen. On a golf course that's not easiest it can get tricky.”
While Mike Weir won The Masters in 2003, Conners and Hughes are bidding to become the fist Canadian to land the spoils in this tournament.
“I feel ready,” declared Conners, who picked up four birdies in five holes at the start of the back nine in his bogey-free 66, of his chances. “I'm going to be a little bit behind starting tomorrow, but I like where my game is at. I feel comfortable in this position.”
World No 1 Dustin Johnson, who finished joint-second here in 2011, dropped eight shots off the lead after a disappointing 73, with four-time major winner Brooks Koepka one further back following a 72.