Headley, who sustained a strained right calf in an infield drill on Feb. 22, got seven at-bats on Wednesday, bouncing between two Minor League games on the Mariners' back fields in Peoria.
"I was really happy with the at-bats and swings I took," Headley said.
Better still, Headley was happy with the overall health of his calf. He had four right-handed at-bats and three from the left side. Headley finished with two singles and a double, though the first hit probably would have gone for a double had he been running hard.
San Diego manager Bud Black said Headley will be in the Padres' starting lineup and playing third base on Thursday against the Giants at the Peoria Sports Complex.
"It was great to see him out there," Black said. "What I liked, he was eager to get out on the field, he felt confident in the calf and he looked good swinging -- a couple of hard-hit balls from both sides of the plate."
Headley struck out in his first at-bat, but he put the ball in play the next six times, as he jumped back and forth between a Triple-A game between the Padres and Mariners and a Double-A game.
"To best honest, I wasn't all that concerned about how I was going to feel," said Headley, who noted the team took a cautious approach to his recovery from the injury. "We had a pretty good idea the calf was going to be fine.
"More than anything, it was just seeing pitching, making adjustments between at-bats and just getting some at-bats under my belt."
Headley, who sustained the injury in an infield rundown drill early in camp, has slowly worked back into game shape, first hitting in the cage, then on the field, taking ground balls and later testing the calf by running during morning practice drills. He passed every test without trepidation.
Black and hitting coach Phil Plantier watched Headley on Wednesday, with Plantier essentially acting as a cruise director, bouncing back and forth to check on Mariners pitching to find Headley a right-hander to face after his first four at-bats were against a left-handed pitcher.
"I was able to swing at the pitches I wanted to swing at," Headley said. "I wasn't getting beat by the fastball. When I'm on the fastball, the offspeed stuff will come. More than anything, it's getting the legs underneath me. I took it really easy today."
Headley didn't play in the field in either game, but he did test the calf when he slid into second base on a clear double, drawing some laughs from the home dugout.
"I hadn't done that in a while, I figured I had to get it out of the way," he said, smiling.
Headley said he has no doubts that he'll be ready for the first game of the season on March 30. He said if he needed additional at-bats, he could always stay behind in Arizona and get at-bats on March 27, a day after the team breaks camp and heads back to San Diego.
The Padres play exhibition games against the Indians at the University of San Diego on March 28-29.
Late Tuesday, the Padres signed right-hander pitcher Hector Ambriz to a Minor League contract. He has a 5.37 ERA over 95 big league games with the Indians (2010) and Astros (2012-13). Ambriz will likely open the season with Triple-A El Paso.