Cienfuegos's first international championship was the 2007 World Youth Championships in Athletics (u18) held in Ostrava, Czech Republic. He was 17 years old at the time, and he finished 8th with a throw of 64,04 m with the 5 kg hammer – a relatively poor result, as his personal best, set four months earlier, was 73,20 m. Ukrainian Andriy Martynyuk emerged victorious with a throw of 76,09 m. Next year, his first year as a junior, he attended the 2008 World Junior Championships in Athletics (u20) in which he finished 12th in the final with a 65,93 m throw with the 6 kg hammer – also a relatively bad performance, his personal best at the time was 76,13 m, set three weeks earlier. Cienfuegos's nerves seemed to be the problem but the expectations only rose in 2009 when he beat Yevgeny Aydamirov's junior world record of 82,62 m and then set a new junior world record with his 82,96 m throw. After more international competition experience, as well as three throws beyond 80 meters, he seemed to have learned how to cope with the pressure. He won the ninth annual European Cup Winter Throwing Championship (u23 group B) with a 73,18 m performance (hammer weight = 7,26 kg). He placed third (79,12 m) at the 2009 European Athletics Junior Championships behind youth World Champion from 2007, Ukrainian Andriy Martynyuk (79,54 m) and Hungarian Ákos Hudi (79,14 m) in one of history's toughest ever junior hammer competitions. Cienfuegos also attended the 2009 World Championships in Athletics and finished 13th in his qualifying group with a 72,01 performance (7,26 kg hammer).