There’s never been more on the line.
Spieth holds a 3-1-1 advantage in their previous encounters this season, but he’ll enter the final round of the PGA Championship two shots behind.
Day is at 15-under 201 as he attempts to break through and win his first major.
“I’m looking at it as it’s going to be a really fun day,” he said. “I can only get better from this, and it should be an exciting challenge playing against Jordan.”
Day and Spieth were most recently paired together in the final round of the Open Championship, when they were in the penultimate group. Spieth edged him, 69-70, but neither qualified for the playoff.