Washington’s defense has dominated in recent weeks. These three drives illustrate how.

Had Washington let Coach Kyle Shanahan’s team tie the game, it would have fit in with the other last-minute lapses from the first half of the season. But in the past three weeks, the group has improved, and on the first two plays, the unit’s two stars of the night — defensive end Chase Young and safety Kam Curl — delivered stops. Four plays later, with the 49ers bottled up, Washington’s players were dancing off the field and into first place in the NFC East.

“That’s what we’ve been working toward,” Coach Ron Rivera said. “Once they gain confidence, then they play with that confidence and they make things happen. That’s important, and that’s the thing that we’re starting to see.”

This four-game winning streak, which put Washington in sole possession of first place, has been keyed by the defense. On Sunday, it tallied two defensive touchdowns and two forced fumbles for the first time since 1997. It has capitalized against mediocre offenses — Cincinnati, Dallas, Pittsburgh and San Francisco — but also made undeniable strides, including on the defensive line and in the linebacker corps to limit big plays, once the Achilles’ heel of this unit.

Rivera believes the unit’s work is far from done. He said they could have been more disciplined by avoiding penalties, plugging rush lanes and containing quarterback Nick Mullens. But he acknowledged the grander vision is coming into focus, and three drives against the 49ers illustrate it.

10:56 left in the second quarter, San Francisco leads 7-0

San Francisco got the ball at its 32-yard line early in the second quarter after a three-and-out. The 49ers were leading, dominating time of possession, and averaging better than five yards per carry. In the past, this was a time when an opponent could gash Washington’s gassed defense for a long scoring drive to extend the lead.

This time, after San Francisco left tackle Trent Williams false-started, defensive coordinator Jack Del Rio dialed up a well-timed blitz. Kevin Pierre-Louis burst into the backfield, sacking quarterback Nick Mullens and setting up second and 24. There was a chance the 49ers could still get back on track — they later converted a few third and longs — because Washington has allowed 13 plays of 40 or more yards this season, worst in the NFL.

But this recent stretch has been different. Sportradar defines “big plays” as runs more than 10 yards or passes more than 20. In the first nine games, Washington allowed six big plays per game. In the last four, it’s been about half that, and on Sunday, the only three they surrendered came in the fourth quarter as San Francisco tried to claw its way back.

On this drive, the key was the rush and coverage working together to prevent an explosive play. Washington derailed the 49ers and got the ball back.

1:50 left in the second quarter, San Francisco leads 7-3

Just before halftime, San Francisco again had good field possession, this time its 38-yard line, and was driving to extend its lead. Instead, on the second play, defensive tackle Daron Payne punched the ball out of Mullen’s hands and Young scooped it up for a score. The power of the play wasn’t a clever scheme or cohesive communication. It was the illustration of pure talent.

While Young said he couldn’t explain the defense’s improvement during the streak, he did theorize the origin of it was Week 10. Washington lost at the Detroit Lions then in part because of Young’s roughing-the-passer penalty late in the fourth quarter. The rookie was distraught afterward, but he said then he wouldn’t have changed his approach because he’d stuck to the core principle of going hard every play. He believes the process hasn’t changed, but the results have.

Everything “builds off everything,” Payne said, describing the defense line. “I’m trying to get there before Chase gets there or [Montez] Sweat gets there or [Ryan] Kerrigan gets there. It’s a competition.”

2:40 left in the fourth quarter, Washington leads 23-15

After the 49ers closed the score to within a touchdown early in the fourth quarter, it seemed like they had the momentum needed to complete a comeback. But Washington stonewalled them over the last four possessions, not only proving it could stand tall in difficult moments, but showing its broader improvement as well.

In those four possessions, when the 49ers had the clock or field position to run the ball, Washington limited them. Defensive coaches have talked often this year about the defense’s struggles to transition from the 3-4 scheme to the 4-3, which asks defensive linemen to play more aggressive and requires different technique.

During the last drive, Washington withstood a strong push. It stopped the 49ers short on a fourth-down conversion attempt, but the increased confidence was best shown a few plays before. San Francisco had hit a 22-yard pass to Kendrick Bourne, an explosive play to set up a possible game-tying score, but it was negated by a holding penalty. Defensive end Montez Sweat walked over, picked up the yellow flag and twirled it like a yellow pompom before handing it back to the referee.