Considering how far the Washington Mystics have come over the past year, Coach Mike Thibault should have been in a better mood Sunday. He has transformed the franchise from one of the WNBA’s bottom feeders into one of its best stories, and the Mystics are on the verge of securing their first playoff berth since 2010.

They’ll just have to wait a little longer to officially punch their ticket.

In a potential preview of what could be waiting for them when the postseason begins later this month, the Mystics lost to the Chicago Sky, 93-79, at Verizon Center.

Washington’s magic number for clinching a playoff spot remains at one, and a win in one of its final three games or a loss by the New York Liberty would put the Mystics over the top. Washington (14-17) closes the regular season Sunday with a game against the Liberty at Verizon Center.

If the playoffs started Monday, the Mystics would be the No. 4 seed and face the Sky (22-9), which has the Eastern Conference’s best record. But Sunday was Washington’s fourth loss to Chicago in five games this year, and the latest setback left Thibault perplexed.

“We’ve got a fight on our hands,” said Thibault, who admitted he was still upset about Washington’s 77-70 loss at last-place Connecticut on Friday night. “I know we only need a magic one to get in. I don’t know if that’s the biggest issue. The odds say that we’re gonna get in the playoffs. It’s more about our mental state and how to approach these types of games and grow up. . . . Growing up has growing pains and we have them.”

The Mystics jumped to a 13-3 lead Sunday by hitting their first five shots of the game, but Washington’s aim grew progressively worse as the first half wore on. It wasn’t long before Chicago’s front court of Elena Delle Donne and Sylvia Fowles began to take over.

Delle Donne, the No. 2 pick in this year’s WNBA draft out of Delaware, didn’t disappoint a sizable contingent of Blue Hens fans in the crowd, scoring 22 points and grabbing seven rebounds. She helped spark a 12-2 Chicago run early in the fourth quarter from which Washington could not recover.

The Mystics cut the deficit to 85-76 with 2 minutes 28 seconds remaining. But Delle Donne put the game away with five straight points, including her second three-pointer of the game.

“We need to be more aware when things aren’t going our way,” forward Monique Currie said. “We can’t make mistakes in bunches.”

Guard Epiphanny Prince had 21 points, Fowles chipped in 13 points and nine rebounds and veteran Swin Cash tallied 16 points for the Sky. Chicago won the rebounding battle, 37-26, and ended up with 20 second-chance points.

“At times, we were really good today and then at times we were really bad,” said Thibault. “That’s kind of who we are right now.”

Added point guard Ivory Latta, who hit six three-pointers and finished with a team-high 18 points and seven assists: “Sometimes I don’t know even know who we are,”

Nonetheless, Thibault made his playoff hopes clear to Chicago Coach Pokey Chatman when the two met at halfcourt for a postgame handshake Sunday.

“We’ll see you in a few weeks,” he said.

SHOCK 98, SILVER STARS 65: Riquna Williams set a WNBA record with 51 points to help Tulsa rout host San Antonio.

The second-year guard out of Miami surpassed the previous record of 47 points set by Phoenix’s Diana Taurasi against Houston on Aug. 10, 2006 and matched by Seattle’s Lauren Jackson against Washington on July 24, 2007.

Williams was 17 for 28 from the field and hit eight three-pointers for Tulsa (11-21). The Silver Stars fell to 11-21.

MERCURY 79, DREAM 71: In Atlanta, Diana Taurasi scored 25 points, Candice Dupree added 15 and Phoenix (17-13) won its third straight. Atlanta is 17-14.