In a historic night at the Diamond League meeting in Monaco, Ciara Mageean ran 4:14.58 to smash Sonia O'Sullivan's 29-year-old Irish record by nearly three seconds, coming in second to Faith Kipyegon's unbelievable new world record time of 4:07.64.
Sifan Hassan had set the previous world best (4:12.33) in 2019, also in Monaco.
32-year-old Mageean was one of seven runners to set new national records in the race, including American Nikki Hiltz (4:16.35), British Laura Muir (4:15.24) and Australian Jessica Hull (4:15.34).
Ethiopian Freweyni Hailu took third place in (4:14.17), a season's best, and Muir was in fourth.
It's the third world record that 29-year-old Kipyegon has broken in the past two months: she also newly holds the records for the 1500m and 5000m.
Kipyegon ran the first 900 meters behind pacemakers Kristie Schoffield and Winnie Nanyondo, splitting 1:02.6 for the first 400m, 2:04.6 for 800m, and 3:06.8 1200m — running the last lap in a jaw-dropping 60.8.
"I do not know how I am doing this because it just keeps going in a really good way," said Kipyegon, who, visibly delighted, was embraced by her competitors after the finish.
"When I started this season, my goal was to just break the 1500m world record. It was still in my head and in my mind. Thank God, I did also the one mile and the 5000m. So many."
"I want to defend my world title at 1500m in Hungary [at the World Athletics Championships], but I am going to double also with 5000m in Budapest."
Mageean will also be headed to Budapest, which she says she feels confident for.
"I think it's been my best season yet," said Mageean, who last year broke O'Sullivan's Irish 1500m record, "I have opened it strong and stayed consistent."
"Today I ran an Irish record over the mile. I am really proud of myself for that. I feel I am in a really good place to go to the World Championships."
"Sometimes when you know you are in a good shape, it's a bit more scary because you really know that you can achieve your goals."
Meanwhile, countrywoman Rhasidat Adeleke came in fourth in the 400m, running 49.99, a stellar performance in the 20-year-old's second-ever professional race. Poland's Natalia Kaczmarek won that race in 49.63.
Adeleke and Mageean's times are both below the qualifying standards for next summer's European Championships and the Paris Olympic games.
Sarah Lavin also shone in Monaco, achieving 12.74 in the 100m hurdles to come in seventh place — just .01 seconds off her personal best, set just a few weeks ago in Stockholm.
All three Irish athletes are expected to return to Ireland next weekend (July 29) for the 123.ie National Senior Track and Field Championships as they prepare for the World Athletics Championships next month.
