Richard Sherman watched his San Francisco 49ers teammates slide on their bellies across the FedEx Field muck late Sunday afternoon, yet he chose not to join them after their 9-0 win over the Washington Redskins. He felt lucky just to emerge healthy from a game he would later dub “The Mud Bowl,” and he wasn’t taking any chances in celebrating.

“I’ve never seen anything like that,” Sherman said of his teammates turning the field into their own water park, but he had also not seen field conditions perhaps this bad over his entire pro career. It reminded him of the last time he played in the stadium as a member of the Seattle Seahawks in a playoff game in January 2013, a game that remains infamous among the Redskins’ fan base. Then-rookie quarterback Robert Griffin III suffered a serious knee injury and the stadium’s surface was widely blamed. Sunday’s slop was bad enough to conjure up those images.

“That’s as bad as I’ve seen,” Sherman said of Sunday’s conditions, which San Francisco overcame to improve to 6-0. “I’ve played in this stadium once before, in the playoffs, and it was pretty bad. That was the year RG III went down with a knee injury. The field was pretty awful. Mostly sand. It was like playing in a sand pit. Today was rain, and everything was going bad.”

Sherman and his defensive teammates woke up to a downpour on Sunday and knew it would fall on them to make plays in what promised to be an ugly game. San Francisco’s defense delivered to end a series of strong Washington drives — it held to force a missed field goal on Washington’s first drive, stopped the Redskins on a fourth-and-one at the 49ers 28-yard line in the second quarter and stripped Adrian Peterson for a fumble deep inside San Francisco territory in the third quarter.

“There’s no excuses. We have to do better,” Washington quarterback Case Keenum said. “The conditions were the same for both teams.”

It was Keenum who was sacked into a puddle of water on the game’s final play by San Francisco defensive end Nick Bosa, who slid across his stomach along with the rest of his teammates in his celebration. “Everybody is a step slower, people can’t make the same cuts or do the exact same things,” Bosa said of the conditions afterward, yet San Francisco appeared to be step ahead of Washington the entire afternoon.

Even as San Francisco went 0-for-4 in the red zone, kicker Robbie Gould adjusted early in the driving rain to shoulder the scoring load. He missed his first field goal but responded with chip shots of 28, 22 and 29 yards. After that first miss, Gould shortened his step and shortened his approach to strike the ball better, he said.

“Today was one of those days where the first team to put points on the board was going to have the advantage,” Gould said.

The 49ers offense, which outgained the Redskins 283-154, made plays in the passing game down the stretch behind quarterback Jimmy Garoppolo and tight end George Kittle. And the defense mounted relentless pressure on Keenum, who threw just 12 passes and was sacked three times. He rarely tested Sherman and the secondary, who by the end of the game had turned the conditions into their advantage. It was the second time that Sherman had endured difficult conditions at FedEx Field, and it was the second time he walked away a winner.

“I think any grass field with this kind of rain, a torrential downpour the whole game, it’s going to be a rough field,” Sherman said. “I know this field’s conditions have been pretty bad, but if it’s raining and it’s grass and dirt, it’s going to turn into mud.”

Read more from The Post: