PITTSBURGH -- The Pittsburgh Steelers dropped a lot of things Monday night at Heinz Field, culminating with the biggest drop of all: their undefeated season and an opportunity to clinch their first playoff berth since 2017.

The Steelers fell to the Washington Football Team 23-17, blowing a 14-point lead that was the second-largest blown lead at home in franchise history.

They were up 14-0 seconds before halftime, but the Steelers lost when up by at least 14 points for only the second time since 2004. Since drafting quarterback Ben Roethlisberger in 2004, the Steelers are 109-2-1 when leading by 14 points at any point, including playoff games.

"I feel like we just kind of relaxed a little," wide receiver James Washington said. "I don't have an explanation right now, but we just have to play better next week. We can't dwell on this. There's plenty of more ball to play."

Tied at 17 with less than five minutes remaining, the Steelers had a chance to score. But with starting kicker Chris Boswell out with a hip injury, the Steelers elected to go for it on fourth-and-1 from the Washington 28.

Roethlisberger targeted rookie Anthony McFarland on a wheel route, but the running back, who has just five catches, couldn't haul it in on a double move, and the Steelers turned over the ball on downs for the second time.

Coach Mike Tomlin confirmed McFarland was the first option on the play. He also said it was his decision to go for it on fourth down rather than putting kicker Matthew Wright, elevated from the practice squad, in a high-pressure situation to kick a 45-yard field goal with the game on the line.

Washington (5-7) responded by doing what the Steelers struggled to do all night: it moved the ball downfield and put points on the board. Quarterback Alex Smith hit Cam Sims on a 29-yard pass on third-and-4 to the Pittsburgh 25, and four plays later, Dustin Hopkins kicked a 45-yard field goal to give Washington a 20-17 lead.

The Steelers had a chance to retake the lead with a two-minute drill, but Montez Sweat tipped Roethlisberger's first pass attempt, and former Steelers linebacker Jon Bostic hauled it in for an interception. Sweat was all over Roethlisberger's quick pass attempts, batting three of them.

"I wasn't good enough," Roethlisberger said. "We didn't put up enough points. We didn't possess the ball long enough."

The game initially was scheduled for Sunday afternoon, but when the Steelers' game against Baltimore was pushed back to Wednesday because of the Ravens' COVID-19 outbreak, the league rescheduled this game for Monday at 5 p.m. ET.

Even with the adjusted schedule, the Steelers still had to prepare on a short week, while Washington had 11 days.

For the second game in a row, the Steelers sputtered against an inferior opponent, their sloppy offense marred by drops -- and it cost them an undefeated season. The Steelers had seven drops, their most in 15 seasons and the most in the NFL this season. Tomlin characterized most of the drops as "routine."

Wide receiver Diontae Johnson, who scored the Steelers' first touchdown, had three drops and leads the league with nine. The three drops tie him with Leonard Fournette and DJ Moore for most in a game this season.

And for the second week in a row, the Steelers couldn't get anything going in the run game. With James Conner still sidelined on the reserve/COVID-19 list, the Steelers rushed for a season-low 21 yards and averaged 1.5 yards per carry. Benny Snell had eight carries for 5 yards -- including three runs that went nowhere at the goal line -- while McFarland had four carries for 15 yards.

"I'm just worried about us fluidly moving the football, whether it's run or pass," Tomlin said. "We move it how we choose to move it. The way that we chose to move it tonight wasn't fluid enough for us to have victory."

The seven-drop performance and sluggish run game comes on the heels of a five-drop outing against the Ravens -- one Tomlin attributed to: "Us sucking."

The Steelers' offense looked more like the 2019 version, continuing a trend that first appeared last week against the Ravens. In the past two games, the Steelers have averaged 4.8 yards per play and 2.6 yards per rush. In 2019, they averaged 4.7 yards per play and 3.7 yards per rush, both 30th in the league.

"We just got to make routine plays routinely," Tomlin said. "I say that often, but there's a lot of truth to it. Got to make routine plays routinely. We're not making them routinely enough right now, so it's affecting our fluidity as a collective group."

The defense nearly shut out Washington in the first half until a field goal in the final seconds. In the second half, Smith picked apart Pittsburgh's zone defense and outscored the Steelers 20-3, including a touchdown drive to open the third in during which Washington overcame back-to-back penalties and got monster third-down conversions from Cam Sims and Steve Sims. The Steelers also committed a penalty on fourth-and-goal, opening the door for Peyton Barber's 1-yard touchdown.

"I thought that touchdown drive to start the second half when we had them third-and-14," Tomlin said, "they hit a perimeter screen for a significant gain to move the chains, kind of started the ball rolling in the wrong way."

The Steelers lost two more key members of their defense. Inside linebacker Robert Spillane suffered an apparent left knee injury in the third quarter, and though his return was listed as questionable, Spillane did not reenter the game. Avery Williamson, whom the team acquired in a trade with the Jets just before the deadline, replaced him. In the fourth quarter, cornerback Joe Haden sustained a possible concussion -- especially problematic with the Steelers already down a starting cornerback with Steve Nelson (knee) inactive.

Though the Steelers are trending in the wrong direction during a grueling three-game, 12-day stretch that culminates with Sunday night's game at Buffalo, Tomlin welcomes the adversity.

"Different points along the journey you get a chance to learn about yourself," he said, "who you are, what you're made of individually and collectively. It takes the journey to reveal that. We're faced with a loss now. We'll get an opportunity to smile in the face of it."

ESPN Stats & Information contributed to this report.