Headley, mired in a 6-for-36 slump with 16 strikeouts, got a rare day off against Giants ace pitcher Tim Lincecum, who threw a shutout, though Headley appeared as a pinch-hitter late in the game.
Headley had appeared in every Padres game (78) since he was promoted from Portland on June 17, making 69 starts in left field, six at third base to go with three pinch-hitting appearances.
Headley didn't bother to fight manager Bud Black when he was first approached about taking the day off.
"This is the first time playing the full 162," Headley said. "The body gets a little worn down and I think [the day off] comes at a good time. It'll hopefully give me a chance to regroup and put together a nice final 14 games.
"The first time is the roughest because you have to figure out what works for you, how to pace yourself."
Headley took a .257 average with nine home runs and 31 RBIs into Sunday's series finale against the Giants at PETCO Park, no doubt hoping to turn around his funk at the plate.
"There are probably a number of things that have gone into it. I have definitely swung at some pitches that I would either like to have back that I've missed on," Headley said, "[or] I have swung at some pitches that were balls. I haven't seen the ball as well. I think I might be a little worn down."
"He's been pressing," Black said. "He's a fellow that really wants to perform, and I think he needs to take a step back. He seems to be in one of those spells [where he's] behind in the count more often than ahead in it."
Headley went though a similar stretch shortly after being recalled from Portland, though he eventually hit his way out of the funk after making an adjustment at the plate to what opposing pitchers were trying to do.
"You can see the general approach a lot of times when you run into a team, or a couple of teams in a row," Headley said. "To me, they were coming in a lot for a while and I made an adjustment to hit that ball. Then they changed and went back away. And now they are coming back in. It's a constant adjustment."