While most eyes were on DeChambeau at the start of the round, Burns managed to steal the spotlight from his playing partner with a brilliant display of skill and control.
Burns shot a record-equalling 62 in Friday’s second round and quickly picked up where he left off with four birdies on the front nine.
A bogey on the ninth tempered his progress, but he picked up two more shots at 14 and 17 to take command.
Burns’ total of 127 shots from rounds two and three (62, 65) is the lowest total across any two rounds in men’s major championship history.
The two-time US Ryder Cup player going on to win his first major would be another extraordinary storyline.
Burns, who finished runner-up at last month’s US Open, was not even planning to play at Birkdale as it clashed with the due date of his second child.
The 29-year-old thought he had “zero per-cent” of going to Merseyside, but when his second child, daughter Belle, arrived on 3 July – almost a fortnight early – his wife Caroline persuaded him to play.
The paternal joy has allowed Burns to play freely and he believes he has nothing to lose on Sunday.
“I’m going to have to go out and execute,” said Burns, who goes out with Fox at 14:20 BST.
“I know that I can accept the outcome, and life’s going to move on. I’ll get to go home and see my family.
“I hope I’m taking some hardware with me, but if I’m not, that’s fine too.”