The American, who failed to spark as he shot three over par through the first two days at Royal Birkdale, found his game as he carded six birdies to move to three under on Saturday.
With nae wind, nae rain and soft greens, the 29-year-old South African went out in 29 strokes under bright skies and came home in 33, making birdies at the first, fourth, fifth, eighth, ninth, 14th, 16th and 17th holes.
Others did know. The 2015 PGA Championship victor Jason Day, having played five groups before Grace, said, "I think this is a good formula to see maybe the first 62 in a major championship". He began the day four over par - he ended it four under, just two shots behind 36-hole leader Jordan Spieth, who had yet to begin his round. Sometimes it helps not knowing these things. "The Open is the event that I love the most so what a special place to get into the history books".
The first weekend score is in the books at the British Open - and it's a good one.
After hard conditions on Friday, Grace was able to take advantage of near-perfect golfing weather on the event's penultimate day to move to within two shots of overnight leader Jordan Spieth.
England's Ian Poulter, runner-up here to Padraig Harrington in 2008, and current US Open champion Brooks Koepka are both three-under. Afterall, his 63 in the final round of the 1973 U.S. Open at Oakmont stood as the gold standard of major golf scores for what feels like forever.
Shaun Norris, playing with a marker after making the cut on the number, shot a 5-under-65 on Royal Birkdale, setting the pace for what could be a day of low scoring.
South Korea's Hyo-Joo Kim holds the record for the lowest round in any major with 61 at the women's Evian Championship in 2014. He shot 64 in the third round of the 2015 PGA Championship. "He never said anything", Grace said.
Playing with Jason Dufner (66), Grace appeared loose down the stretch and laughed a few times at Dufner comments.
"I think I'm in a position where it can be very advantageous, just everything I've gone through, the good, the bad and everything in the middle".