The Liberty cast aside the reigning WNBA champions Sunday afternoon, continuing a late-summer surge.

Tina Charles scored 21 points, Shavonte Zellous added 19 and Epiphanny Prince had 18 points and five assists in an 83-69 victory over the Los Angeles Sparks at Madison Square Garden. The Liberty has won three in a row and five of seven.

“We were just locked in and doing great on defense, and that set the tone,” Charles said.

“I think we’re starting to understand who we are,” coach Bill Laimbeer said. “We’re passing some tests now, and if we can continue on this train, then we’ll be OK.”

The Liberty (15-12) trailed by 11 points with less than seven minutes left in the second quarter before finishing the period on a 22-2 run. Prince’s three-pointer with just over four minutes left in the first half gave the Liberty the lead for good.

Laimbeer said of the comeback: “They got off to a tremendous start, made every shot and put us on our heels a little bit . . . The game plan was to keep them on the perimeter, and once we figured that out and stuck to it, they didn’t make the shots anymore. We got the rebounds and we ran the ball down their throats in the second quarter and got a lead.”

Said Charles, “We know we’re a really good team, but it’s about putting it together for 40 minutes. We were able to do that collectively for the last three quarters.”

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Zellous played a big role in the turnaround, scoring 17 of her points after the first quarter. He has averaged 18.3 points in the last three games.

“She’s a great competitor,” Laimbeer said. “She made a couple of big shots when they were trying to get back in the game. Overall, she’s an outstanding player this year.”

The Sparks (19-8) own the second-best record in the league and possess a potent offense that features Candace Parker (14 points) and Nneka Ogwumike (12).

Said Charles, “We forced them to take a lot of jump shots and closed down the middle.”

The Liberty moved the ball well, as 19 of its 31 made baskets came off an assist.

Said Zellous: “We preach about trying to go in the right direction to get where we want to go, and that’s what we’re doing as a group.”