Sifan Hassan’s world mile record of 4:12.33 and Samuel Tefera’s 3:31.04 world indoor 1500m record have been ratified.

Hassan, the European record holder in the 3000m, 5000m and half marathon, signalled her intentions to claim the standard over the mile distance on the eve of the Herculis EBS IAAF Diamond League meeting in Monaco, declaring that she was intending to run “three or four seconds” faster than her previous mile lifetime best.

She came up a bit short of that prediction on 12 July, but still crossed the line as the fastest miler of all time, clocking 4:12.33 to break a record which had stood for 23 years.

“I knew I could run fast but the first 800 was a bit slow, so after that I wasn’t thinking it would be a world record,” Hassan said. “When I crossed the line I was so surprised.”

Indeed, her opening 800m of 2:08.5 was nearly a second-and-a-half outside of the pace that propelled Svetlana Masterkova to her 4:12.56 record in Zurich in 1996. But Hassan forged on. Energised by the pulsating cheers of the near-capacity crowd at Stade Louis II, Hassan ran alone from about 1000 metres onwards, covering the final 800m in under 2:01 and the final 400m in just a few ticks over 60 seconds.

Tefera, the world indoor 1500m champion, upstaged Ethiopian compatriot Yomif Kejelcha at the IAAF World Indoor Tour meeting in Birmingham on 16 February to clip 0.14 from the previous record set by Hicham El Guerrouj in 1997, more than two years before Tefera was born.

While the focus was on Kejelcha, who came within 0.01 of the world indoor mile record just seven days before, Tefera, 19, patiently waited, tucked in behind Kejelcha as he tracked the pacemakers during the early laps. He then overtook his rival with less than 100 metres remaining and ran hard to the line, leaving Kejelcha helpless in his wake.

“I can’t believe that,” said Tefera, who won’t turn 20 until 23 October. “I’m delighted with the outcome and to have the world record is a special feeling.”