Neil Walker back in the lineup but baby is on deck

SAN FRANCISCO — Mets second baseman Neil Walker returned to the starting lineup in Saturday’s 9-5 win over the Giants after missing four games with a stiff lower back. But his return could be brief, and it has nothing to do with his back.

If Walker’s wife does not go into labor with the couple’s first child, she will be induced tomorrow. Walker intends to be present at the birth, so he will play in Sunday’s series finale before hopping on a red-eye flight to suburban Pittsburgh after the game.

Of course, those plans could change quickly if Walker’s wife goes into labor.

Either way, Walker could wind up missing part of a critical series against the Cardinals, a three-game set that begins Tuesday. The Mets are 4 1⁄2 games behind the Cardinals for the last National League wild-card spot.

Walker had been the Mets’ hottest hitter when his back tightened up, and after returning, he made his presence felt. He walked, singled twice, scored twice and made a diving stop at second base in the fifth to keep the tying run off the board Saturday.

“I got challenged pretty good today,” said Walker, who missed four games in June with a similar back issue. “Scored from second twice, dove two or three times, and it feels good.

“Similar to last time, just needed to give it a couple of days and I’m good to go.”

Henderson returns

After a two-month absence, righthanded reliever Jim Henderson rejoined the Mets on Saturday after being activated from the disabled list. He replaced the struggling Erik Goeddel, who was optioned to Triple-A Las Vegas. Henderson went on the DL with right biceps tendinitis on June 21. He was 1-2 with a 4.26 ERA in 31 appearances, though he was excellent early in the season. Said Terry Collins: “Right now, our bullpen can use a fresh arm.” Henderson’s rehab hit a snag because of a hamstring injury, but in recent days, Collins said he received favorable reports about Henderson’s velocity.