Kaysay was seventh at the world juniors last year and took silver medal at this year's African Youth Championships in Warri, but this time he won the one that mattered, becoming Ethiopia's second WYC boys' 2000m steeplechase champion after Legese Lamiso in 2007.
The 17-year-old finished ahead of two Kenyans, Nicholas Bett, who also dips inside the previous world youth's best with a Kenyan youth record 5:20.92 and Justus Lagat, who also sets a personal best in third place with 5:30.00.
Kenya's Alexander Lerionka Sampao took the Bronze medal in boys' 400m with a lifetime best time of 46.78 seconds ahead of teammate Ian Mutuku, who finished fourth in 47.02 seconds.
South Africa's Julia du Plessis and Morocco's Rhizlane Siba settled for joint bronze medals with a final height of 1.79 metres in the Girls' High Jump won by Australian Eleanor Patterson (1.88m).
Nigeria's Ejowvokoghene Divine Oduduru, the sprinter who ran the whole 100m yesterday after the semifinal was recalled for a false start, won his 200m Heat in a lifetime best time of 21.24.
Kenyans Daisy Jepkemei, the world junior champion (6:24.73), Rosefline Chepngetich (6:46.32), Ethiopians Bezuayehu Mohamed and Weynshet Ansa all advance to Sunday's girls' 2000 metres steeplechase Final.
Nigeria’s Edidiong Ofonime Odiong finished fifth in a lifetime best 54.14 seconds in the girls' 400m event won by Great Britain’s Sabrina Bakare who smashed her 400m PB for the second time in two days to win in 52.77 seconds.
400m Girls Final
- Sabrina BAKARE (GBR) 52.77 PB
- Olivia BAKER (USA) 53.38
- Tiffany JAMES (JAMAICA) 53.56
- Nguyen THI OANH (VIETNAM) 53.80 PB
- Edidiong Ofonime ODIONG (NIGERIA) 54.14 PB
- Nanako MATSUMOTO (JAPAN) 54.59
- Anastasiya KUDRYAVTSEVA (RUSSIA) 54.69 PB
- Luca PALÁSTI (HUNGARY) 54.81
400m Boys Final
- Martin MANLEY (JAMAICA) 45.89 WYL
- Ryan CLARK (USA) 46.46
- Alexander Lerionka SAMPAO (KENYA) 46.78 PB
- Ian MUTUKU (KENYA) 47.02
2000m Boys Steeplechase final
- Meresa KAHSAY (ETHIOPIA) 5:19.99 WYB
- Nicholas Kiptonui BETT (KENYA) 5:20.92 PB
- Justus Kipkorir LAGAT (KENYA) 5:30.00 PB
- Hicham CHEMLAL (MOROCCO) 5:32.92 PB
- Micheale ATSBAHA (ETHIOPIA) 5:36.64 PB
Triple Jump Girls Final
- Florentina MARINCU (ROMANIA) 13.75
- Rong WANG (CHINA) 13.69
- Keturah ORJI (USA) 13.69
- Nubia SOARES (BRAZIL) 13.60
- Marie Josée EBWEA BILE (FRANCE) 13.31
High Jump Girls Final
- Eleanor PATTERSON (AUSTRALIA) 1.88m
- Erika FURLANI (ITALY) 1.82m
- Rhizlane SIBA (MOROCCO) 1.79m
- Julia DU PLESSIS (SOUTH AFRICA) 1.79m
- Ana Paula DE OLIVEIRA (BRAZIL) 1.79m