Olympic champion Keely Hodgkinson produced a dominant display to win the women's 800-metre at the Diamond League meet in Lausanne, with British team-mate Georgia Hunter Bell finishing third.
Hodgkinson, who has been recovering from a hamstring injury, returned after a 376-day absence in Silesia last weekend to set a world-leading run of one minute and 54.74 seconds, just behind her own national record.
With the World Championships in Tokyo coming up next month, Hodgkinson laid down another marker as she made a strong finish in wet conditions to set a new meeting record of 1:55.69.
Hunter Bell had been in second place down the home straight but faded in the closing metres as Switzerland's Audrey Werro ran her down to clock 1:57.55.
Hodgkinson, 23, had looked in control from the opening part of the race, sitting second behind the pacemaker at the bell, which she took in 56.04 seconds.
With only Prudence Sekgodiso for company heading into the final 300-metres, Hodgkinson soon pulled clear of the South African to coast towards another impressive victory.
"[I feel] a little bit relieved," Hodgkinson told the BBC.
"I felt like this race was definitely going to be more of a challenge, but taking on a pace like that you've just got to run and forget about everybody else.
"I'm glad it paid off. I feel like I've really backed up my 1:54 with a solid 1:55. We are seeing improvements all the time, so I'm happy.
"I couldn't have asked for a better start -- I'm a bit in shock myself. I train well, I train really hard for moments like this, but when it all comes together it makes it extra special.
"[My coach] Trevor [Painter] said to me a few weeks ago 'you are actually ahead of schedule. I wanted you to be here by the time we are in Tokyo,' so to be here now is amazing.
"Hopefully we can stay healthy and build on top of what we've got, and let's see what can happen."
Hodgkinson's training partner Hunter Bell, meanwhile, must now decide whether to have another crack at the 800-metre in Tokyo or focus on the 1,500-metre where she would be looking to add to her Olympic bronze medal from Paris.
"I wanted a bit quicker but it was hard today, hard to recover from the race a few days ago," she said.
"I don't know [what distance], I'm going to decide this week. I'm running out of time to make a decision. Every day I change my mind."
Conditions worsened as the events went on, with Elise Thorner (9:21.74) finishing fifth in the women's 3,000-metre steeplechase, which was run through a downpour.
Morgan Lake placed fifth in the women's high jump following three failures at 1.91-metres.
With the run-up so wet, Ukraine's Olympic champion Yaroslava Mahuchikh decided to retire after two missed attempts.
In the women's 200-metre, Dina Asher-Smith (22.64) was fifth and Daryll Neita (22.73) seventh, with American Brittany Brown winning in 22.23 seconds.
In the men's 800-metre, Max Burgin attacked around the final bend but then faded over the closing stages as he finished fourth in 1.43.44. Olympic champion Emmanuel Wanyonyi lost out to American Josh Hoey.
Alastair Chalmers ran 49.92 seconds as he was fifth in the men's 400-metre hurdles.
Men's 100-metre Olympic champion Noah Lyles came second as Jamaica's Oblique Seville clocked 9.87 seconds, with Britain's Zharnel Hughes fifth in 10.09.