Emmanuel Wanyonyi broke the long-standing men's 1,000m world record on his debut at the rarely run distance in Friday's Diamond League meeting in Monaco, with Great Britain's Jake Wightman finishing second.
Wightman, 31, pushed Wanyonyi hard to the line but had to settle for the runners-up spot as the 21-year-old Kenyan won in a record time of two minutes 11.83 seconds.
Wanyonyi is the reigning Olympic and world 800m champion and shaved 0.13 seconds off the previous record, which had been held by compatriot Noah Ngeny since 1999.
Wightman, the 2022 1500m world champion, clocked a personal best of two minutes 12.77 seconds at the Stade Louis II, moving him to fifth on the world all-time list.
The next Diamond League meeting is in London on 18 July.
GB's Ben Pattison was fifth in the race and Algeria's Olympic bronze medallist Djamel Sedjati took third place.
Speaking after the race, Wanyonyi said he was "so happy" to achieve the record, but he dismissed any thoughts of attempting to break the 800m mark set by fellow Kenyan David Rudisha at London 2012.
"I don't want to talk about the world record in the 800m. I first want to run fast and improve my personal best," he said.
"Let me keep quiet. Actions speak louder than words."
Wightman said he wished he could have "surprised" Wanyonyi, but added: "I was nearly there. This was just a long 800, so I wanted to go through quickly and try and hang on for as long as I could."
In the men's high jump, Britain's Kimani Jack placed second on his Diamond League debut with a clearance of 2.30m.
The 22-year-old failed to go further at 2.32m, while Ukraine's world and European indoor champion Oleh Doroshchuk cleared it at the first attempt to take victory. India's Sarvesh Kushare was third with 2.26m.
GB's Matthew Hudson-Smith finished fourth in the men's 400m, placing fourth in 44.22 seconds as world champion Collen Kebinatshipi set a Diamond League record of 43.44.
Botswana's Kebinatshipi, who beat Americans Jacory Patterson and Rai Benjamin into second and third place respectively, celebrated his victory with push-ups inspired by countryman Isaac Makwala.
Meanwhile, British Olympic triathlon champion Alex Yee finished 12th in the men's 5,000m at his first Diamond League event for seven years.
In the men's 100m, Jamaican world champion Oblique Seville held off American Jordan Anthony with a time of 9.88 seconds in the final race of the night, with Emmanuel Eseme of Cameroon taking third.
Saint Lucian Julien Alfred, the Olympic 100m champion, achieved a standout win in the women's 200m, crossing the line ahead of Adaejah Hodge of the British Virgin Islands and American Gabby Thomas with a time of 21.51 seconds.
That makes Alfred the third fastest woman of all time over the distance, behind only world record holder Florence Griffith Joyner (21.34) and Shericka Jackson (21.41).
World record holder Armand Duplantis secured a meeting record of 6.07m in the pole vault, with Frenchman Baptiste Thiery and Australian Kurtis Marschall both clearing 5.85m to finish second and third respectively
