Natalie Whitty broke the Guernsey 1500m record after running at time of 4:29.00 at the island's second Intertrust Grand Prix meeting at Footes Lane on Tuesday.
Her time took 2.74 seconds off the previous record set by Sarah Mercier last July.
But Mercier was also celebrating after the 22-year-old set a personal best of 16:55.54 in the 5000m, taking 38 seconds off her personal best.
It was also good enough to qualify for next summer's Commonwealth Games.
Mercier becomes only the second woman from Guernsey to run under 17 minutes over the distance.
"I knew I was in good shape and I knew that I could probably do that time fairly early on in the season," Whitty told BBC Guernsey.
"But for my first outdoor race of the season I was quite shocked.
"All of last year I was hoping for the island record over 800m to be honest, I wasn't expecting to get the 1,500m, but it's very nice to have."