It was raining steadily at Shea Stadium at 12:30 p.m., so the Mets’ potentially season-deciding matchup with the Marlins this afternoon remained up in the air. Whenever the game is played, Jerry Manuel has some surprises in store for the Mets’ lineup behind ace Johan Santana, who is pitching on three days rest for just the second time in his career.

Upset by the Mets’ lifeless bats in a 6-1 loss Friday, Manuel is moving David Wright to the cleanup spot and Carlos Beltran to the No. 2 hole, among several changes. Manuel also is starting Ramon Castro behind the plate because Castro works better with Santana.

Manuel shook up his team because the Mets could be eliminated today if they lose to Florida and both Philadelphia and Milwaukee win. Manuel is hoping Santana can work his magic after compiling an 8-0 record and 2.26 ERA in his past 16 starts. Santana also is 2-0 with a 3.21 ERA in two starts against the Marlins this season.

Santana will be faced by Florida ace Ricky Nolasco, a 15-game winner who has won four consecutive decisions. Nolasco is 1-1 with a 3.71 ERA against the Mets in five starts this season and 2-2 with a 7.85 ERA lifetime at Shea Stadium.

The overall lineup for the 88-72 Mets:

Jose Reyes SS

Carlos Beltran CF

Carlos Delgado 1B

David Wright 3B

Daniel Murphy LF

Ramon Martinez 2B

Ryan Church RF

Ramon Castro C

Johan Santana LHP (15-7, 2.64)

The 83-76 Marlins are going with:

Hanley Ramirez SS

John Baker C

Jorge Cantu 1B

Josh Willingham LF

Dan Uggla 2B

Cody Ross CF

Wes Helms 3B

Jeremy Hermida RF

Ricky Nolasco RHP (15-7, 3.55)

Game time: 1:25 p.m. (rain delayed).

TV: SNY.