Sabrina Ionescu added 24 points and Kayla Thornton had 20 for New York (14-3), which has won 10 of its last 11 games, including a 93-80 victory in the first meeting between the teams on Thursday.
Dearica Hamby scored 20 points to lead Los Angeles (4-13). Zia Cooke contributed 14 points off the bench while Stephanie Talbot had 11 points, eight rebounds and seven assists, the latter two team highs.
Los Angeles is without Cameron Brink, who was lost for the season after tearing the anterior cruciate ligament in her left knee, while Azura Stevens is still sidelined after having surgery on her left arm. Lexie Brown was also out because of an illness.
The Sparks signed Queen Egbo to a hardship contract. Egbo arrived in New York late Friday night and without any prep time to make her a custom jersey, she wore No. 44 with white tape over the jersey name.
Stewart made sure the Liberty would sweep the two games. She had an incredible first half on both ends of the floor. Stewart scored 24 points and five assists to go along with five blocks. She became the first player in WNBA history to have over 20 points, five assists and five blocks in a half.
Stewart, who also had three steals, made eight of her 10 shots from the field in the opening 20 minutes.
“We were letting them off the hook a little bit,” Stewart said. “Make sure I demanded the ball in the post.”
Thornton made a career-high six three-pointers, including five in the second half.
“Every time it goes up I know it’s going in,” Liberty coach Sandy Brondello said of Thornton. “She’s always going to give us great effort.”
New York trailed 31-23 early in the second quarter before the reigning MVP took over. Stewart outscored the Sparks 19-13 the rest of the period as the Liberty built a 54-44 lead at the half.
The Liberty put the game away in the third quarter and up 20, Stewart had a chase-down block on Talbot that drew the crowd to its feet. That matched Stewart’s career-high of six blocks.
New York was still missing guard Courtney Vandersloot, who has missed seven games to be with her mother, who passed away over the weekend. Vandersloot did return to the team Saturday and was warming up before the game.
“It’s been a tough time for her and her family,” Brondello said. “She’s back in town, but we’re just ramping her up a little bit. ”
The Liberty were also still playing without Nyara Sabally (back) and Betnijah Laney-Hamilton (knee).
The Sparks continue their seven-game trip at Phoenix on Friday night. The Liberty play at Atlanta on Sunday.