Batting third and playing left field, Bay exited for a defensive replacement in the seventh inning.
The three-time All-star pulled a single to left field in the opening inning and grounded out to third base leading off the fourth.
Sidelined since late March with a strained rib cage, Bay drew an intentional walk from Charlotte's Alex Koronis with one out and a runner on third in the sixth. He went first-to-third on Wilmer Flores' single to left field but was stranded when Stefan Welch popped out.
Bay also had one putout in left field, snaring Christopher Murrill's fly ball in the fifth.
The 32-year-old is scheduled to make another Florida State League appearance Sunday when St. Lucie hosts the Fort Myers Miracle. If everything goes smoothly, Mets manager Terry Collins said Bay could rejoin the team as early as Tuesday for the series opener against the Houston Astros.
"We'll see where we're at after that," Collins told MLB.com. "He's been swinging, he's been hitting, he's been running. He's done everything. Now it's just game at-bats."
Signed as a free agent in December 2009, Bay played 95 games in his first season in New York. He batted .259 with six homers, 47 RBIs and 10 stolen bases before crashing into the left-field wall at Dodger Stadium on July 25 and spending the rest of the season on the disabled with a concussion.
Catcher Ronny Paulino threw out a runner trying to steal second base but went 0-for-3 with a pair of strikeouts Saturday and is hitless in five at-bats during his rehab assignment.