WASHINGTON — If there was a surprise in Knicks coach David Fizdale’s starting lineup preseason opener, it was a small one — but telling nevertheless.

Marcus Morris, who signed a one-year, $15 million deal in July, was to start at small forward over 2018 lottery pick Kevin Knox when the Knicks opened shop Monday night against the Wizards at Capital One Arena.

Indications are this is the way it’s going to go when the season opens Oct. 23 in San Antonio.

“I may mix it up a few times before this whole thing goes down,’’ Fizdale said before tipoff. “I thought those guys overall played the best at practice and throughout camp.”

Knox started last preseason as a rookie, but came off the bench when the regular season began. With the Knicks in tank mode, Knox inherited the starting job for good in mid-December. Now, Fizdale needs to post victories.

“There’s a chance he can start in the preseason again,” Fizdale said. “Nothing is in stone.”

Knox expressed optimism the battle isn’t over while accepting his new bench role. Fizdale said he’d spot Knox at the 3 and some shooting guard.

“I think that’s one of our strong suits this year is going to be the players coming off the bench,’’ Knox said. “I think our bench is going to give us a nice little spark. There’s a lot of guys still fighting for jobs. Coach hasn’t finalized any lineups. There’s a lot of guys still competing for spots. So nothing really solidified until the regular season. We’ve all got preseason to compete,”

However, Knox will be OK if he’s the sixth man.

“I’m very comfortable coming off the bench,’’ Knox said. “It’s going to be a good spark for us. Some of the guys coming off are really talented. I think it’ll be pretty good for the team.”

As a 19-year-old rookie, Knox averaged 12.8 points but shot 37 percent and struggled on defense. He’s come back from the offseason with a bigger upper body.

“I feel he’s more comfortable,” Fizdale said. “Things aren’t surprising him as much anymore. His shot has improved. He shortened his stroke, simplified it. Defensively he’s been better.”

Knox likes the idea of playing some shooting guard, especially with Reggie Bullock (back) and Damyean Dotson (shoulder) out for the preseason.

“[Shooting guard] and [small forward] are really the same,’’ the 6-foot-8 Knox said. “Just work on my defense, getting better at that area. Our offense is all fluid, flow, people can really play any different position. I talked to Fiz and I’m cool with it.”

Knox came on from the 3-point line in the final month last season and finished out at 34.3 percent from deep.

“I’m trying to shoot 40 [percent],’’ Knox said. “I think that’s a good number for me. I think my shot’s gotten a lot better. I’ve just got to eliminate bad shots and hit the open ones.”

Morris had dabbled at power forward in recent seasons, but Fizdale has enough big men. The 30-year-old, known for his toughness, will be cemented at the 3.

“That’s what we’re going to play [him] more at this year,” Fizdale said. “We’re going to take him back to when he first came in the league. We like idea of size of that position.”

With Dennis Smith Jr. out with a strained back, Fizdale went the obvious route with Elfrid Payton as starting point guard. Rookie RJ Barrett was to start at shooting guard, Julius Randle at power forward and Mitchell Robinson at center. Those four slots were as expected.

It’s a big lineup but not one full of outside shooters. Barrett has struggled from 3, Payton is not known as a perimeter threat and Robinson almost never takes jumpers.

“With our big lineup, all those guys are capable of shooting the basketball,’’ Fizdale said.

Fizdale wouldn’t reveal Payton as starting point guard Sunday, leading to speculation that team brass wanted to see more of Frank Ntilikina because of the upcoming deadline to exercise his fourth-year contract option. But Ntilikina came off the bench.

“His competitiveness, he’s got a serious competitive gene,” Fizdale said of Payton. “He’s never out of a possession offensively or defensively. It just stands out.”

Smith said he’s unsure when he will return. The Knicks play host to the Wizards on Friday. Smith missed 10 of the final 14 games last season with a disk issue. He said this injury is different because it’s not “dealing with the nerve.”

“It’s up to coach and whatever the training staff decides,” Smith said. “If they think I’m ready, I’ll play. It’s unfortunate — small bump in the road.”