The world 10,000m champion clocked 12min 35.36sec at the Stade Louis II to shatter Ethiopian Kenenisa Bekele's previous record.
Ugandan Joshua Cheptegei ensured a thrilling return for competitive athletics on Friday as he shattered the much-vaunted 16-year-old 5,000m world record at the Monaco Diamond League.
Cheptegei's astonishing display capped a warm welcome back for track and field for a season almost wiped out by the coronavirus pandemic, with fellow world champions Noah Lyles and Karsten Warholm also shining on the track.
Lyles had worn a black glove on his right hand and raised his fist at the start of the 200m to show his support for recent anti-racism protests.
In perfect conditions, with little wind and temperatures of 27 degrees Celsius (81F), Cheptegei clocked 12min 35.36sec to shatter Ethiopian legend Kenenisa Bekele's previous best of 12:37.35, set in 2004.
"I've tried to improve on my speed," smiled Cheptegei when asked what he had been working on since his world gold medal showing in the 10,000m in Doha in September.
"It took a lot of mind setting to keep being motivated this year because so many people are staying at home, but you have to stay motivated."
The Ugandan added: "I pushed myself, I had the right staff with me, the right coach. I'm also usually based in Europe, but being based in Uganda with my family was actually great."
Following exhibition events in Oslo and Zurich in June and July, the Diamond League meeting in Monaco marked the start of the competitive season.
Meetings in Eugene, London, Paris, Rabat, Gateshead and Shanghai have all cancelled because of coronavirus.
Running in front of a reduced capacity of 5,000 masked spectators in line with COVID-19 restrictions, music blared out as World Athletics debuted a "bespoke atmosphere creation system" to enhance the experience for the athletes, the spectators and the broadcast audience in the absence of a full crowd.
Warholm showed no sign of coronavirus-induced rustiness as he led from gun to tape to clock a meet record of 47.10sec in the men's 400m hurdles, the first time he has run the event since he won his second world title in Doha.
"It's a great start," said the Norwegian. "I'm happy to be back. It's great seeing some audience... competitors at my side."
The joy of victory!
Lyles raises black-gloved fist
World 200m champion Lyles also had no problems in his race, sweeping to a convincing victory in 19.76sec.
Raising a black-gloved fist to the air when introduced to the crowd, the win was the perfect tonic for Lyles, who has admitted to psychological problems worsened by the "perfect storm" of the COVID-19 outbreak, the Black Lives Matter movement and the postponement of the Tokyo Olympics at which he was hotly tipped for success.
"It's a lot better to be out here competing instead of being in your backyard," said Lyles.
"I have high expectations for myself so I'd say the race got the Noah stamp of approval but not the Noah satisfaction stamp!"
A loaded women's 5,000m field witnessed a battle royale between Kenyan world champion Hellen Obiri and Ethiopian Letesenbet Gidey.
After world 1,500m and 10,000m double gold medallist Sifan Hassan dropped out of the running, Gidey took up the fight, leading Obiri through the bell.
But the Kenyan responded magnificently, sprinting away for the win in a meet record of 14:22.12.
Obiri's teammate and fellow world champion Timothy Cheruiyot also held off Norway's Jakob Ingebrigtsen for a thrilling win in the men's 1500m, taking the victory by 0.23sec in 3:28.45.
American Donavan Brazier made no mistake in the men's 800m, bettering his world lead to 1:43.15.
However, there was no such success for US compatriot and world 110m hurdles champion Grant Holloway, who could only finish fourth (13.19sec) in a race won by Cuban-born Spaniard Orlando Ortega (13.11).
Earlier in the day, French pole vaulter Valentin Lavillenie was ruled out of competition after testing positive for COVID-19.
That competition was claimed by Sweden's world champion Mondo Duplantis with a best of 6.00m. His American arch-rival Sam Hendricks missed the event as his poles hadn't arrived.
In the other two field events on show, Venezuela's Yulimar Rojas won the women's triple jump with a best of 14.27m, while world heptathlon champion Katarina Johnson-Thompson of Britain could only finish sixth (1.84m) in a women's high jump competition won by Ukrainian Yaroslava Mahuchikh (1.98).
Six more Diamond League meets are currently scheduled, in Stockholm, Lausanne, Brussels, Rome, Doha and a yet-to-be-decided venue in China, running from August 23 until October 17.