Anna Moesch's mashing of her own personal best 100m free for the first sub-52 continental Americas record and all-time No2 performance of 51.94 in the last session of AP Race's London International on Monday evening doubtless landed with a thud Down Under.

Is Dolphin dominance of the 4x100m facing a serious threat on the way to LA2028 and a stab at an historic match of Olympic bull runs in the event?

We're two years out from an Olympics where the hosts hope to break Australia's iron grip on the sprint free relay. A lot could happen before the fame is lit, of course, but you can bet on the Olympic-champion 4x100 free nation at all four of the past Games, London 2012 to Paris 2024, harnessing every fast fin, fluke and flipper in its school and sorority of sprinters as Los Angeles looms larger.

Moesch, the latest member of coach Todd DeSorbo's University of Virginia women's team to make a big breakthrough to the helm of global speed, left her blocks at the London Aquatics Centre as No9 all-time American and 41st all-time globally, her best of 53.25 from last month back home on Pro Tour in Florida having been shaved back to 53.23 in heats Monday morning in London.

Before that, her top time was a 53.54, clocked at U.S. nationals in June last year in the season she left her teens behind her. Those three 53sec swims were her only entries in the all-time top 200 performances by Americans until she rocketed to a new status last night.

Sailing right over the 52s, Moesch leap-frogged eight Americans, four of whom boast Olympic and World-Championship gold in their pantheons, the fastest of them until Monday evening in London Simone Manuel, the 2016 Olympic 100m free champion who had held the Americas record at 52.04 since claiming the World title in Gwangju back in 2019.

The splits compared, showing two of the fastest splits in history, set in the past few days, the other belonging to 2025 World 100m free champion Marrit Steenbergen:

24.83 - 26.88 - 51.71 Sarah Sjöström (SWE) Budapest - 23/07/2017
25.18 - 26.76 - 51.94 Anna Moesch (USA) London - 25/05/2026
24.81 - 27.17 - 52.04 Simone Manuel (USA) Gwangju - 26/07/2019
25.46 - 26.61 - 52.07 Britta Steffen (GER) - Rome 31/07/2009
24.98 - 27.08 - 52.06 Cate Campbell (AUS)- Brisbane 02/07/2016
25.51 - 26.62 - 52.13 Marrit Steenbergen (NED) - Monte Carlo 23/05/2026 (The latter swum on Mare Nostrum Tour, more on which will be added with our round-up of weekend action in the Vortex today)

The London Race:

Only Sarah Sjöström, the double Olympic 50-100m freestyle sprint champion and 51.71 World-record holder from Sweden, has ever swum faster than Moesch's march to great expectations one the way to LA2028.

A Dam Building - The New All-Time Women's 100m Free Top 10:

The American's thunderbolt of progression couples with a Pan Pacs selection policy based on 2025 efforts means she may not meet Australian rivals in a 100m free race until World titles in 2027 at the earliest, and even then would need to beat two of her UVA teammates in racing, Kate Douglass and Gretchen Walsh, respectively the Olympic and World 200m breaststroke champion, and the World champion and multi-record breaker in the 100m butterfly.

Here's the top 6 - five of them still active, on the all-time USA ranking:

51.94 Amma Moesche - London, 25/05/2026
52.04 Simone Manuel - Gwangju 26/07/2019
52.29 Torri Huske - Paris 31/07/2024
52.56 Kate Douglass Indianapolis 19/06/2024
52.59 Mallory Comerford Budapest 23/07/2017 (retired)
52.78 Gretchen Walsh Indianapolis 03/06/2025
52.79 Rylee Erisman (17 this year) - Otopeni 21/08/2025

All barring Moesch (who also clocked a 24.27 to win the 50 free on the first day of the meet last Saturday), are selected to race at Pan Pacs in Irvine. She is now one of two American women to have broken through to a place in the global all-time top 3 rankings this season who is not rostered to race at the biggest clash of Dolphins and Eagles this summer. The other is Isabelle Stadden, who this year has risen to 3rd after all-time in the 100m back and 4th all-time in the 200 back. Regardless of any impressive ranking, both improvers face a tough domestic battle even to make the USA team for LA 2028 in solo events.

As for the relay, the women's 4x100m freestyle had been in Australia's grip since the first of their last four Olympic victories, at London 12. Rio, Tokyo and Paris delivered more gold, while the World titles of 2015, 2019, 2022, 2023 and 2025 also went to Dolphin quartets.

The World record has been Australia's since 2014, five standards (2014, 2016, 2018, 2021 and 2023) taking the mark from 3:30.98 down to 3:27.96, the time clocked by Mollie O'Callaghan (52.08) Shayna Jack (51.69) Meg Harris (52.29) and Emma McKeon (51.90) for the world title in Fukuoka. The 2018 mark, which delivered Commonwealth Gold at the home Gold Coast Games, included the faster 100m free split in history: Cate Campbell, 51.00!

With one under 52, and five on 52s in solo racing spring 2026, the USA is edging closer to mounting a serious challenge to Australia at a home Games in 2028. The last time the two nations clashed in a global title chase, it was a close call, and came down to gold for Australia when the clock stopped at a calmer pace for the Dolphins than their nations six best efforts, the fastest four the swiftest performances ever, the USA 5th all-time with a 3:30.05 Americans record for silver at Paris 2024 behind Australia's 3:28.92, all-time No2 behind their world record.

Races like this, of course, prove that paper exercises are good for getting the barbie going - Singapore 2025:

• Mollie O'Callaghan (52.79) Meg Harris (51.87) Milla Jansen (52.89) Olivia Wunsch (53.05) - 3:30.60 AUS
• Simone Manuel (53.09) Kate Douglass (51.90) Erin Gemmell (53.17) Torri Huske (52.88) 3:31.04 USA

Even so, teams have to be looking at quartets with at least two sub-52 splits, if not more, and anything over as close to flat as possible, in the hunt for LA2028 gold. The USA has not held the world record in the event since 2002, but looks back on a history of most Olympic crowns since it all began in 1912 - 14, with Australia on 6 and looking for seventh heaven in 2028.

Victory for Australia would draw the Dolphins level with the all-time record run of straight Olympic golds by a single nation in the 4x100m free. The holders are the USA, whose women claimed the title in 1960, '64, '68, '72, and, with that famous 'Last Gold' in Montreal, '76, the latter a standout in the book of swimming lore:

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More coverage later in the day as we catch up from a few days out of action through illness.