DOHA, Qatar — Dalilah Muhammad had no idea whether she had even won when she crossed the finish line on Friday night at Khalifa International Stadium. She had to look at the scoreboard to learn the results, she said, and it was only then that she realized what she had accomplished.

Muhammad, 29, had not only won the women’s 400-meter hurdles title at the track and field world championships — she had broken her own world record, too.

“It feels good to have it come together when it matters most,” she said.

Muhammad held off Sydney McLaughlin, her young American challenger, in the final meters to win in 52.16 seconds, four hundredths of a second better than the world record she had set in July at the United States championships. McLaughlin, 20, was runner-up in 52.23, which was a personal best and the third-fastest time ever.

“She’s amazing,” McLaughlin said of Muhammad, who grew up in Queens. “She’s been doing this a long time, and I’m just constantly trying to learn from her.”