A heavy rainstorm turned the O.co Coliseum into an unplayable muck Friday night and forced the postponement of the Mariners’ game against the Oakland A’s.

The storm hit early in the morning when the infield was uncovered. Day-long efforts to repair the damage were unsuccessful and prompted the postponement as the 7:05 p.m. start time approached.

“The field’s not playable, that’s for sure,” said Seattle manager Lloyd McClendon, who walked the field in consultation with the umpires and officials from both clubs.

“Very soft. That’s probably the worst conditions I’ve seen in all my years in baseball. It’s not safe. It was just a safety issue more than anything. They made the right decision.”

The game will be rescheduled at a later date, probably as part of a day/night doubleheader when the Mariners return for a May 5-7 series. That decision requires agreement from the players’ union.

First things first: The Mariners didn’t sound confident the field will be repaired in time for the scheduled 1:05 p.m. game Saturday.

“We’ll see what happens,” general manager Jack Zduriencik said. “They say they’re going to work on it all night. What that means, we’ll have to see. But they have a lot of work to do to get it ready.”

The A’s chose to leave the field uncovered overnight in hopes it would help the infield to dry after recent heavy rains.

“The field has taken a significant hit all week,” said David Rinetti, the A’s vice president for stadium operations. “We’ve been working with a weather consultant to get as much up-to-date information as possible.

“We had information (Thursday) night that there was going to be a break in the storm. And because of that, we wanted to use that opportunity to help dry out the field.

“Unfortunately, we were wrong on the amount of rain, and we got about one-third of an inch of rain. We did not have the tarp on the field. We got here this morning, the infield was under water.”

Rinetti did not identify the consultant.