Spieth has now won three of the four majors on offer after his victory at The Open at Royal Birkdale last month, and is goes in search of the grand slam at Quail Hollow this week.
Tiger Woods currently holds the record for the youngest player to win a career grand slam, but Spieth can take the honour over the next four days, and is feeling calm about the situation.
"I'm about as free and relaxed at a major than I think I've ever felt, " said Spieth, the world number two. "Do I have to be the youngest? No, I don't feel that kind of pressure.
"It's not a burning desire to have to be the youngest to do something, and that would be the only reason there would be added expectations".
Thunderstorms and rain are forecast for the next four days, and Spieth admits how he performs with the driver with be key to his chances at the North Carolina course.
"This is going to be one of the most challenging tracks I think that we've played," said Spieth, whose best finish in the US PGA is second in 2015. "The rough is brutal. I need to drive the ball better than I've been driving it to have a chance to win this week."