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 at home in franchise history.

After being up 14-0 with seconds until halftime, the Steelers surrendered just their second loss when up by at least 14 points 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.

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

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

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

Roethlisberger and 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 in the quarterback's lone interception of the night. Sweat was all over Roethlisberger's quick pass attempts Monday, batting three of them.

It was another painful weekday performance in a game that was rescheduled because of the COVID-19 ripple effect. Monday's game was initially scheduled for Sunday afternoon, but when the Steelers' game against the Baltimore Ravens was eventually pushed back to Wednesday, the league rescheduled this game for Monday afternoon 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 to ready for the league's only undefeated team.

For second game in a row, the Steelers sputtered against an inferior opponent, playing sloppy offense marred by drops -- and this time, it cost them an undefeated season. The Steelers had seven drops against Washington, their most in the past 15 seasons and the most in the NFL this season.

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

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, averaging 1.5 yards per play in the run game. 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.

The seven-drop performance and sluggish run game comes on the heels of a five-drop outing against the Ravens -- one Mike Tomlin expressed his disgust with after the close win by attributing the drops and red zone failures to one thing: "Us sucking."

The Steelers' offense looked more like its 2019 version Monday night, 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.

The Steelers' defense nearly shut out Washington in the first half until they scored a field goal in the final seconds of the half. In the second half, Smith picked apart Pittsburgh's zone defense and outscored the Steelers 20-3 in the second half.

The Steelers also lost two more key members of their defense throughout the course of Monday's loss. Inside linebacker Robert Spillane sustained an apparent left knee injury in the third quarter, and though his return was listed as questionable, Spillane did not re-enter the game. Avery Williamson, whom the team acquired in a trade with the Jets just before the deadline, replaced him. Then, 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.

ESPN Stats & Information contributed to this report.