Sykes, who finished with 20 points, caught an inbounds pass from Natasha Cloud in the lane and put it in before the buzzer, ending the Liberty's eight-game winning streak and any chance to get the top seed in the playoffs.
Cloud and Sykes said they were going to throw the lob no matter what, as it gave them the best chance to win and not go to overtime again against New York. The Mystics lost in OT to the Liberty in late June.
“I'll be the person receiving the lob,” Sykes said. “It was one of those things we had our minds made up and not trying not to go to overtime again.”
The teams will meet in the first round of the WNBA playoffs, with Game 1 on Friday in New York.
“We started the game and we want to send a message, ‘You’re going to have to see us all series long,’” Cloud said. “'You have to go through a really good team still. A team that’s hungry, a team full of dogs.' ... Let it be known this is going to be a really good series.”
Washington (19-21) turned a 71-67 lead to start the fourth quarter into a double-digit advantage. New York was down 84-74 with 4:41 left when Sabrina Ionescu was fouled hard on a drive by Tianna Hawkins. The foul was upgraded to a flagrant one. Ionescu made both free throws to start a 14-4 burst to tie the game on Stewart's layup with 21.5 seconds left.
Cloud worked the clock down before getting the ball to Delle Donne, who drove baseline before getting blocked by Stewart.
Ionescu scored 20 points and Jonquel Jones added 19 for the Liberty (32-8). Cloud contributed 17 points for the Mystics.
It was a tight first half, with the teams tied at 50 at the break. Washington built its lead to 69-57 late in the third quarter before New York closed the period on a 10-2 run to get within four heading into the fourth.
“It feels good to come back and keep the whole team together,” said Laney, who is averaging 12.8 points, 3.2 rebounds and 2.5 assists this season.
The Liberty raised a banner celebrating their Commissioner's Cup championship before the game.
“It's always special. This organization from the beginning has had some close opportunities to win some championships in the early days,” Liberty coach Sandy Brondello said. “It's still a title that's really special. Hopefully, keeps motivating us to put more up.”
New York also brought back many of its former stars, including Teresa Weatherspoon, Swin Cash, Sue Wicks and Kym Hampton, much to the delight of the crowd.