Kristi Toliver, shown during a June game, reached 1,000 assists in Wednesday’s loss. (Terrance Williams/For The Washington Post)

In less than a week, the Washington Mystics have gone from mighty to meek defensively, a troubling trend with WNBA playoff seeding starting to take shape.

The latest unraveling came during Wednesday’s 106-89 loss to the Atlanta Dream at Capital One Arena, where the decibel level peaked thanks to a cacophony of screams from thousands of campers.

Cheering, however, came only in short bursts, with the Mystics trailing by double figures for most of the second half amid myriad breakdowns that led to the most points Washington has permitted this season.

The Mystics (12-8) had not yielded triple digits over their first 19 games; the latest loss came three days after the first-place Seattle Storm beat visiting Washington, 97-91.

“Most nights when you score 89 points, you should probably win,” Mystics Coach Mike Thibault said. “But when you play defense as badly as we did, you don’t give yourself a chance to do that.”

The Dream (10-9) shot 60 percent from the field, including 61 percent from three-point range, to drop Washington to fifth place with more than a third of the season to go. The Mystics entered the game in third with aspirations of moving closer to a top-two seed and an automatic berth to the semifinals of the WNBA playoffs.

But it was the Dream that looked far more playoff ready, thanks in part to the starting backcourt of Renee Montgomery (21 points) and Tiffany Hayes (21 points) combining to make 9 of 13 attempts from beyond the arc.

Forward Angel McCoughtry scored a game-high 24 points to lead four Atlanta starters with at least 21 points.

McCoughtry is a two-time WNBA scoring champion who sat out last season to rest her mind and body. The four-time all-star led Atlanta to the WNBA Finals three times in her first eight seasons.

This year, McCoughtry came back to a remade team, including first-year Coach Nicki Collen, a former Louisville assistant who was instrumental in recruiting McCoughtry to play for the Cardinals.

“Let [her teammates] do their thing, and it kind of takes attention off of me a little bit, and then that’s when I can come down and get my spots,” McCoughtry said. “I like to sneak and get them, to get my sneaky points in there.”

Washington got within 51-43 on the heels of five straight points from guard Natasha Cloud late in the first half. McCoughtry took over from there, scoring 15 of Atlanta’s next 16 points, including six in a row to begin the third quarter for a 65-52 lead.

McCoughtry reached 20 points for the sixth time this season and for the fifth time in her past eight games against Washington.

She also was involved in a collision that forced Mystics starting center LaToya Sanders from Wednesday’s game early in the third quarter. As McCoughtry was landing following a layup, her forearm and elbow struck Sanders in the cheek, leading officials to review the play.

McCoughtry received a technical foul, and Sanders had to be helped to the locker room.

The severity of the injury is unclear, according to Thibault, who indicated that playing without one of the league’s top shot blockers was hardly to blame for the overall lack of defensive effort and execution.

“If I could grade ourselves on defense today, it was a complete F,” Cloud said. “We had our defensive scheme, but we need to take pride in our defense. There’s no reason in the last two games that our opponents are scoring 106 and 97 points. We’re scoring the basketball. That’s the scary thing. We’re scoring the basketball and still losing games, so something’s got to switch for us as a team.”

Cloud led the Mystics with 17 points on 7-for-11 shooting. She was the only Washington player to make more than half of her shots.

Elena Delle Donne added 16 points but went 5 for 14 from the field, and guard Kristi Toliver, typically proficient from beyond the arc, missed four of her five three-point attempts.

The first quarter proved particularly eventful for Toliver, who collected her 1,000th career assist with 6:15 to play on a pass to Delle Donne.

Toliver became the 24th player in WNBA history to reach 1,000 assists. But five minutes after she achieved that milestone, officials assessed a technical foul on Toliver for voicing her displeasure over a non-call.

The Mystics are among a cluster of clubs within three games of first place during a highly competitive season in which the top two seeds might not be determined until perhaps the league’s final weekend.

“Every game is a dogfight, so you’ve got to be ready to fight it out like a playoff game,” Delle Donne said. “It’s definitely wide open. I feel like the standings don’t mean a thing right now.”