Four-time Olympic champion Mo Farah broke the one-hour world record on his return to the track at Friday's Diamond League meeting in Brussels.
Farah ran 21,330m, bettering the record of 21,285m set by Haile Gebrselassie in 2007.
It is the 37-year-old Briton's first world record outdoors.
"It isn't supposed to be easy to break a world record, but I can tell you that it was really hard. The record stood for a very long time," said Farah.
"So that says a lot. I was very excited to be back on the track. My first meet back on the track was what was driving me."
In the rarely run one-hour race athletes try to cover as much distance as possible in 60 minutes.
Earlier on Friday, Sifan Hassan of the Netherlands set a new world record in the women's race. Her 18,930m effort surpassed Dire Tune's mark of 18,517m, set in 2008.
Farah switched to road running after the Rio Olympics but was returning to the track in his bid to compete in the 10,000m at next year's postponed Tokyo Games.
Competing for the first time since October's Chicago Marathon, Farah pulled away alongside Belgium's Bashir Abdi with 30 minutes left.
The pair's effort looked in doubt as they fell behind Gebrselassie's record pace with no fans in the stadium to drive them on, but they went ahead again as the final quarter of the race began.
Abdi briefly took the lead, but in the end six-time world champion Farah kicked away and won the race with ease.
He completed over 53 laps at an average pace of 67 seconds per lap to become the 12th athlete to hold the record.
"At a certain point, with just 10 laps to go, it became tough so I was happy that Bashir took the lead," Farah added.
"However, I felt great with just one minute to go. I kept believing in my speed so I knew I had a good chance to take this win. A last fast lap is still my best tactic."
Farah will return to road racing when he competes in the Antrim Coast Half Marathon on 12 September.
He will then act as a pace-setter for Kenya's world record holder Eliud Kipchoge and Ethiopian Kenenisa Bekele at the delayed London Marathon on 4 October.
Also competing in Brussels, Britain's world heptathlon champion Katarina Johnson-Thompson ran a season's-best time of 13.57 seconds to finish fourth in the 100m hurdles. The 27-year-old later came sixth in the high jump, reaching 1.84m.
Kenyan Faith Kipyegon, the reigning Olympic 1500m champion, missed out on the 1,000m record by less than a second.
The 26-year-old finished in two minutes 29.92 seconds, with Russian Svetlana Masterkova's record having stood at 2:28.98 since 1996.
In the men's 1500m, Norway's Jakob Ingebrigtsen - the event's European record holder - sailed to an easy victory in 3:30.69 while Sweden's Armand Duplantis cleared an impressive 6m to win the pole vault, surpassing the meeting record of 5.96m set by France's Renaud Lavillenie.
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