Aerial Powers wasn’t interested in excuses Saturday night. The Washington Mystics had just suffered their first loss of the season in a lackluster manner that was quite different from the brand of basketball that has come to define the defending WNBA champions.

The Mystics rode a wave of energy and the league’s best offense to become the last remaining undefeated team. A third game in five days, however, seemed to take its toll as the Mystics lost, 88-86, to the Chicago Sky in Bradenton, Fla.

Cheyenne Parker made a layup with 5.9 seconds remaining for the game-winning basket after Diamond DeShields drove the baseline and drew a help defender off Parker. The Mystics failed to get a shot on their final possession when Emma Meesseman declined to shoot and turned the ball over trying to force a baseline pass instead.

“Honestly, we beat ourselves,” Powers said. “I don’t think Chicago beat us. We didn’t start off with the energy we usually do . . . and that’s on us.

“I’m not one to make excuses. We just have to bring [the energy] next game. I’m not sure why. I’m not going to sit here and say we’re tired. Everybody’s tired. We’re all in the same predicament. . . . We heard Chicago celebrating. I think that’s kind of what we needed, kind of a slap in the face.”

The teams went back and forth from the opening tip. With just nine available players, Washington (3-1) exerted a ton of energy to push its lead to 60-52 off a Leilani Mitchell layup with 3:35 left in the third quarter. But the Mystics sagged from there, and the score was tied at 62 entering the fourth.

The Mystics shot just 41.9 percent from the field and simply didn’t have the same tempo they displayed in their previous three games.

The defense also seemed to move at three-quarters speed as Chicago (3-1) shot 51.4 percent from the field and 48 percent from behind the three-point arc.

Ariel Atkins scored a game-high 24 points for the Mystics, Powers added 20 points, and Myisha Hines-Allen finished with 13 points and 12 rebounds.

Parker and Gabby Williams led the Sky with 16 points apiece. Allie Quigley chipped in 15 points, and Kahleah Copper added 14.

The Sky scored 20 points off 14 Washington turnovers.

“You saw the good and the bad of our team tonight,” Mystics Coach/General Manager Mike Thibault said. “Saw us make some great plays. Saw us make some awful plays, awful decisions. Our turnovers were unbelievably costly. . . . I think we’re tired.”

The Mystics rallied from an ugly first quarter to take a 37-35 lead into halftime. Washington, which largely scored at will in its first three games, shot just 35.3 percent from the field in those opening 10 minutes, and a pair of layups by Parker closed an 8-0 run that put Chicago up 20-15 at the end of the quarter.

The Mystics awakened in the second quarter, when the trio of Hines-Allen, Atkins and Powers did the heavy lifting. Washington shot 2 for 9 from three-point range in the first half en route to shooting 8 for 22 (36.4 percent) on the night, but the interior began to open up after a pair of midrange jumpers from Essence Carson. A 7-2 run capped by a three-point play by Meesseman gave the defending champions their two-point halftime advantage.

Meesseman continued to struggle offensively after recently acknowledging that her shot hasn’t been falling this season.

The Mystics expected the 2019 WNBA Finals MVP to be their No. 1 offensive option in 2020 with four projected starters unavailable, but she has been anything but. Her all-around game has been sharp — Meesseman entered Saturday averaging a career-high 5.0 assists — but her 12.0 points per game entering Saturday would be her lowest average over a full season since 2015.

She finished 4 for 10 from the field in a game in which the Mystics could have used more from their most accomplished player. She finally got going late in the fourth quarter and finished with nine points, nine rebounds and six assists, but it wasn’t enough. Her turnover on the final play sealed the outcome.

“Basketball is 40 minutes,” Atkins said plainly. “I don’t think we locked in for 40 minutes.”

Note: Mystics forward Tianna Hawkins missed her third consecutive game with a lumbar sprain in her back.

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