History, however, says he's anything but a sure thing.
This is the seventh time a multiple major winner has held the 54-hole lead in a major since 2009. But five of the previous six (including Spieth at the 2016 Masters) did not win.
That's just one of the things You Oughta Know going into the final round of the year's third major. Following are some others:
• Spieth has converted eight of his last nine 54-hole leads or co-leads on the PGA Tour. However, he is just 50 percent - two-for-four - converting 54-hole leads or co-leads in majors, and he failed to convert his previous major opportunity (2016 Masters).
• One trend in Spieth's favor: No player has won an Open at Royal Birkdale who was more than 2 back entering final round.
• Spieth does lead a lot of rounds, be it majors or regular tournaments. This is his 14th major round led or co-led in his career (13 have come since the beginning of 2015). It's also his seventh consecutive round with a lead or co-lead (he won the Travelers in wire-to-wire fashion).
• Spieth's 65 was his fifth career bogey-free round in a major. It's the first time that Spieth has had multiple bogey-free rounds in the same major. It's also the first time Spieth (65-69-65) has begun a major with three rounds in the 60s.
• If Spieth does win, he would become just the second player (joining Jack Nicklaus) to win three legs of the Grand Slam before age 24.
• He would become the youngest champion of The Open since Seve Ballesteros in 1979.
• He would become the first player with 10 PGA Tour wins including three majors before age 24 (Spieth will turn 24 on July 27).
• If he completes the Grand Slam at this year's PGA Champonship, he would become the youngest Grand Slam winner.
Some facts about Spieth's challengers:
• Matt Kuchar, who trails Spieth by three, fits the profile of recent Open winners. He is 39; the average age of last six Open winners is 38.5. He is ranked 18th in World; the average rank of last five Open winners is 16.8.
• Brooks Koepka (six shots back) has been under par in eight of his last nine major rounds, including Saturday's 2-under 68.
• Koepka, who won the U.S. Open last month, is trying to become the seventh player to win the U.S. and British Opens in the same year.
• After needing only 21 putts in his opening round, Koepka has logged a total of 60 in Rounds 2 and 3.
• Austin Connelly, a 20-year-old Canadian making his major championship debut, birdied his last two holes Saturday to shoot 66. He is seven shots back.
• Connelly is making only his seventh career start in a PGA Tour-sanctioned event (and first this season).
• Branden Grace (seven shots back) shot 62 on Saturday, the lowest 18-hole score in major championship history.
• That was a 12-shot improvement over his second round (he made only one birdie Friday).
• Grace is still looking for his first major win, but he does have four top-5 finishes in majors (all since the beginning of 2015).
• Grace was 10 shots back entering the third round, and only one Open champion has overcome that kind of 36-hole deficit (G. Duncan, 1920).
• Hideki Matsuyama's 66 tied his lowest career weekend round in any major. He trails by seven.
• This is Matsuyama's third time inside the top 5 through 54 holes in a major.
Some other notables:
• Dustin Johnson (trails by 8): His 64 was his lowest career round in any major.
• Henrik Stenson (trails by 8) His 65 was his fourth career round of 65 or better in a major.
• Rory McIlroy (trails by 9): In shooting 1-under 69 on Saturday, he birdied three of his first five holes, but he played the back nine in 1 over.
(Information provided by the Golf Channel Editorial Research Dept.)