Kenya's Mary Keitany during the IAAF/EDF Energy World Half Marathon Championships in Birmingham (Getty Images) © Copyright
Keitany, who cruised to the world title over the distance in Birmingham last autumn, dominated the proceedings clocking 1:07:14, more than two minutes clear of her nearest rival.
Regassa, who will celebrate his 20th birthday on 18 January, clocked 59:19, bettering his 59:36 career best set two years ago. Only World record holder Samuel Wanjiru has run faster while younger than 20 with his 59:16 in Rotterdam in 2005, at the time a World record.
Keitany, who set an African record of 1:06:36 at the World championships in October, had already built a solid field by 10 kilomtres, reaching the marker in 31:15, some 50 seconds ahead of her closest pursuers, a chase pack led by her compatriot Philes Ongori, the World silver medallist.
Keitany closed with a time of 1:07:14, incredibly the slowest performance of her last four half marathons, but still the 10th fastest performance of all-time. Keitany produced five of the 10 fastest runs ever over the distance.
In a very competitive final, Ongori crossed the line in second place with a time of 1:09:16, followed by 2008 Boston Marathon champion Dire Tune, who clocked 1:09:19.
In the men's race, Regassa pushed the pace from the start and crossed 10 kilometres in 28:14, ahead of Sammy Kitwara, the fastest man in the field with a 58:58 PB, the fourth time ever. With one kilometre to go Regassa made a strong move to clinch the victory. Kitwara Held on for second in 59:34.
Another little-known Ethiopian, Lelisa Benti, broke the one hour wall by just one second (59:59) to finish third while another five men ran under 61 minutes.
The race started at 3:30 pm in windy but war conditions, with the temperature at 25 C.
"If they would have started just a couple of hour later, both world records could have been broken," said Italian manager Gianni Demadonna.
Alberto Zorzi for the IAAF
Leading Results -
1. Tilahun Regassa (Eth) 59:19
2. Sammy Kitwara (Ken) 59:34
3. Lelisa Benti (Eth) 59:59
4. Wilson Kiprotich (Ken) 1:00:04
5. Willy Mwangi (Ken) 1:00:07
6. Wilson Chebet (Ken) 1:00:31
7. Kiplimo Kimutai (Ken) 1:00:41
8. Fabiano Joseph (Tan) 1:00:53
1. Mary Keitany (Ken) 1:07:14
2. Philes Ongori (Ken) 1:09:16
3. Dire Tune (Eth) 1:09:19
4. Aselefech Mergia (Eth) 1:09:21
5. Amane Gobena (Eth) 1:09:24
6. Wude Ayalew (Eth) 1:09:25
7. Mare Dibaba (Azb) 1:09:38
8. Peninah Arusei (Ken) 1:09:39