Saint Louis took the lead just 11 minutes into the match when former Notre Dame midfielder Amanda Cinalli slotted home a pass from Eniola Aluko past goalie Karina LeBlanc.
Athletica goalie Hope Solo held off the Sol, stopping Marta (twice), Han Duan, Brittany Bock and Aya Miyama.
Despite the win, the Athletica still trails Los Angeles by 14 points but has three games in hand.
The Sol do not return to action until July 23 at FC Gold Pride.
July 8 in Carson, Calif.
Saint Louis 1 Los Angeles 0. Goal: Cinalli (Aluko) 11.
Saint Louis -- Solo, Weber, Ellertson, Larsson, Logterman, Chalupny, Fletcher, Cinalli (Tancredi, 78), Stoia, Angie Woznuk (McNeill, 77), Aluko (91+: Niki Cross).
Los Angeles -- LeBlanc, Makoski, Cox, Bock, Larkin (Wagner, 46), Zerboni (Patterson, 78), Abily, Boxx, Miyama, Duan (Bogus, 46), Marta.
Yellow cards: Los Angeles -- Marta 70; Saint Louis - McNeill 83.
Referee: Margaret Domka.