Keely Hodgkinson says she is aiming for a new world record after breaking the British 800m best at the UK Athletics Indoor Championships in Birmingham.
The 23-year-year-old, who took Olympic gold in 2024, clocked 1:56.33 in the event's heats to beat her own national record by almost one second.
It was the fastest time in a women's 800m race in 24 years and the third-fastest time in history.
Having announced beforehand that she would not compete in Sunday's final because she is due to take to the track at the Hauts-de-France Pas-de-Calais Trophee in France on Thursday, Hodgkinson described the run as "a personal challenge".
"I had to come to qualify for the worlds [in Poland next month] and that is why I was only doing one round," she said.
"But it was a good test. It is three years since I ran indoors, so I knew I had to go out there and stay focused.
"We didn't set out to run a world lead, but I started well and just kept it going. It was a nice surprise. It was a really strong day."
'I feel like it's my record to break'
Asked about targeting Jolanda Ceplak's indoor world record of 1:55.82 set in 2002, Hodgkinson said: "I have been very vocal in the past about wanting to get it.
"I feel like it is my record to break. We'll give it a good go."
Dina Asher‑Smith was another star to deliver a stunning performance on the first day of the event in Birmingham, claiming the women's 60m title with a run of 7.05 seconds - a tenth of a second ahead of Amy Hunt, to set a new championships record.
Speaking afterwards, the 30-year-old said she had been "feeling great for this entire indoor season", adding: "Sometimes you just have to be patient, get race-sharp and wait for the times to come."
In the men's 60m, world and European indoor champion Jeremiah Azu, 24, retained his UK title, reaching the line in a season's best of 6.56 seconds.
Molly Caudery reclaimed the women's pole vault crown by clearing a height of 4.65m with Owen Heard taking the men's with an effort of 5.55m.
Lucy Hadaway took victory in the women's long jump with a leap of 6.45m, while 15.45m saw Tito Odunaike take the men's triple jump.
In the women's 60m hurdles, a personal best of 8.05 seconds secured victory for Abigail Pawlett, with Daniel Goriola taking the men's equivalent in a season's best 7.78.
Madeline Down crossed the line first in the women's para 60m final with a time of 8.24 seconds, and a time of 6.93 seconds was enough for Kevin Santos to take the men's title.
You can watch day two of the UK Indoor Athletics Championships, on Sunday, on BBC iPlayer, the BBC Sport app and website. Events run from 11:20 to 16:30.