Bouanga converted a penalty after a questionable foul call against Miki Yamane in the 35th minute, and that goal turned out to be the winner in the latest edition of the El Tráfico rivalry.
LAFC rebounded from the worst start in franchise history (2-3-1) for its eighth win in 22 meetings with the Galaxy, including five of the last seven matchups between the rivals separated by 12 miles of freeway.
Julián Aude scored his first MLS goal in the first half for the rejuvenated Galaxy, which suffered their first loss after a 3-0-3 start.
Galaxy goalkeeper John McCarthy made seven saves against his former team while LAFC controlled long stretches of play in the second half, but the Galaxy couldn’t counter.
Hugo Lloris made three saves as LAFC improved to 3-0-1 at home this season.
LAFC went ahead in the fourth minute when Mateusz Bogusz’s corner flicked off Ilie Sánchez’s head and went straight to Tillman, who deflected it in with his body at the far post.
Tillman’s score was the MLS-worst sixth goal given up by the Galaxy off set pieces this season.
Aude evened it in the 29th minute after a mad scramble that started with his shot off the post. Aude had another shot blocked by Jesús David Murillo before the 21-year-old Argentine left back finally slotted a shot past Lloris into the left corner.
But Bouanga was awarded a penalty shot moments later when he went down with slight contact from Yamane, infuriating the Galaxy. After the referee upheld his own decision on video review, the 2023 Golden Boot winner drove it straight down the middle past a diving McCarthy, the surprise MVP of the MLS Cup Final in late 2022 to secure LAFC’s first league championship.
The Galaxy struggled to generate scoring chances after halftime. Bouanga had a chance to put it away with 10 minutes left in regulation, but he badly missed a wide-open net high after a crossing pass perfectly delivered to his right foot.
LAFC didn’t have Carlos Vela on its roster for the first time in the rivalry’s history. The former MLS MVP and Golden Boot winner is sitting at home as an unsigned free agent while LAFC struggles to score, although the club added 39-year-old striker Kei Kamara last week and is expected to sign French star Olivier Giroud soon.