Lauren Kleppin, who has designs on competing for the United States in the
Kleppin, 25, finished in 2 hours 28 minutes 48 seconds, trimming more than 13 minutes from her previous-best marathon time.
Kleppin ran with winner Amane Gobena and four other Ethiopian competitors for the first seven miles and then appeared to fall off the pace.
"I wanted to run my own race, so I was trying to figure out in my head what I was capable of," Kleppin said.
Kleppin rallied, returned to the pack and led for part of the race before Gobena and Tigist Tufa took control.
Kleppin's finish gave her confidence as she looks toward 2016.
The U.S. Olympic trials for the men's and women's marathon will be held in Los Angeles, though not on the Stadium to the Sea course used by the L.A. Marathon.
American Kristen Fryburg-Zaitz, 33, finished sixth in 2:39:42.
Americans Gabriel Proctor and Aaron Braun made their marathon debuts and finished sixth and seventh, respectively, in the men's race.
Proctor, 23, finished in 2:16:17, Braun, 26, finished in 2:19:51.
Stephan Shay was ninth in 2:25:20, Adam Roach was 10th in 2:32:38.
Defending men's champion Erick Mose of Kenya had hoped to become the third male runner to win the LA Marathon in consecutive years.
But Mose, 27, fell off the pace about midway through the race. He finished third in 2:12:56, about three minutes slower than his winning time of 2:09:43 last year.
Ethiopian Gebo Burka won in 2:10:37 and Kenyan Lani Rutto was second in 2:10:48.
Mose said he felt no effects from a hamstring injury that slowed him for part of his training, but
He rallied for a podium finish.
"I was not going to go quit," he said. "I just kept going and did my best.
"I will be back next year."
Joshua George's victory in the men's wheelchair race ended Krige Schabort's four-year winning streak.
George, 29, finished in 1:33:11.
"A good way to kick off the season," he said.
Rafael Botello Jimenez of Spain was second in 1:38:03, Schabort third in 1:38:04.
Susannah Scaroni, 22, defended her title in the women's wheelchair race. She won in 1:54:54.