The 49ers remained undefeated with their 9-0 win Sunday in Washington DC, but in this case, the field stole the spotlight from the actual game being played.

FedEx Field produced a backyard game of mud football, with heavy rain coming down and water splashing up every time a player ran through the puddle. The conditions called for an ugly game, but Robert Saleh's 49ers defense handled the adversity admirably.

Former 49ers safety Donte Whitner, who dealt with plenty of tough conditions over his 11-year NFL career, believes San Francisco played about as well as a team could on such a mess of a field.

"I give them an A-plus," Whitner, now a 49ers analyst for NBC Sports Bay Area, said Sunday. "Playing in these type of conditions, understanding that it's not going to be a game about who has the best players, who has the best game plan ... it's gonna come down to willpower and understanding it's going to be a four-quarter game of runs, direct runs with a guy like Adrian Peterson.

"Going into it, you know it's gonna be an ugly, muddy football game where the most mentally strong team that makes the least amount of mistakes wins."

Defensive backs might be at the biggest disadvantage with a wet field. Cornerbacks and safeties easily can lose their footing while backpedaling in the mud. The same goes for trying to change direction and react to a receiver's route.

 

It's not like receivers have an easy task running through the mud and loose surface, but knowing your route automatically puts you ahead of the defense. It's hard enough for a DB to read if a receiver is running in on a quick slant or cutting off a deep route for a comeback.

Now try it in the rain.

"You have to react on the run, and who knows what kind of footing you're gonna have, so you have to keep your knees bent, keep your hips bent so you can get out of those breaks," Whitner said. "If not, you'll give up big plays."

The 49ers didn't give up too many big plays at all Sunday. They held quarterback Case Keenum to 77 passing yards -- their second straight week where a QB was held under 100 -- and Adrian Peterson couldn't bust a back-breaking run, his longest being 15 yards.

Mud football games might be fun when you're with your friends at the park, but it's a different story in the NFL. Every week counts, and neither team was wishing for this type of weather.

[RELATED: Watch Bosa's slip-and-slide sack celly to end 49ers' win]

"It's just miserable for everybody," Whitner said. "The most mentally strong team that makes the least amount of mistakes is gonna win the game."

On Sunday, that team was the 49ers, who continued to look like real contenders.