The poster girl of Malaysian athletics crossed the finish line in Nashville in 51.79 seconds, breaking her record of 51.80 set last year in California.
Florida-based Shereen has 28 days left to run 50.95s in order to qualify for the Paris Olympics.
Shereen and sprinter Azeem Fahmi are on the wildcard list for the Paris Olympics, but only one slot is available if they do not qualify on merit.
Currently ranked 91st in the world and third in Asia, she needs to be among the world’s top 48 400m racers by the end of June to see Olympic action.
Shereen, the national women’s 200m and 400m indoor record holder, will return home on June 8 to compete in the Malaysian Open Athletics Championships a week later.
Due to a lack of serious competition to Shereen and Azeem locally, the Malaysian Athletics Federation has requested for their entry to a bronze-level meet in Kazakhstan on June 22 to make Paris on merit.
In yesterday’s race at the Music City Track Carnival at Middle Tennessee State University, the reigning SEA Games 400m gold medallist packed a scorching pace on the rain-soaked track to finish second in her heat.
Shereen finished second overall in the professional category that had 19 runners in three heats, with the fastest athlete clocking 51.67s.
The carnival involved track and field competition for professionals stacked with Olympians, youth and open meet for all-comers and an elite level high school meeting.
Her coach, Derrick White, said he was pleased that Shereen had executed the race plan well despite the cold and rain.
He said it rained before the race, causing the inside of the track to be flooded.
“Breaking the national record and doing a personal best under such conditions is a great achievement,” said White, who is the head coach and CEO of Life Speed Athletics.
Ipoh-born Shereen, 25, has been training in Florida under White since June last year, and grabbed the bronze medal in the 400m five months later at the Hangzhou Asian Games.
Her mother, Olympian Josephine Mary, thanked White for bringing Shereen to new heights in the one-lap race.
She said White had been constantly teaching her daughter new techniques to improve herself in speed and fitness.
“I am glad she’s running faster and dreaming big,” said Josephine, a former middle-distance sensation and national elite coach. Her husband, Samson’s 800m timing of 1:48.29s in 1989 remains the oldest record in SEA Games men’s athletics.