He qualified for the 2002 IAAF World Cross Country Championships held in Belfast, where he finished tenth in the junior race.

It was in this occasion that he joined the management of the Italian Gianni Demadonna, and started to be coached by Renato Canova, that developed his talent from the youth category up to the current international level.

At the 2002 IAAF World Cross Country Championships in Lausanne he fared slightly better, finishing 7th in the junior race.

[9] At the Zevenheuvelenloop 15K race, he was off the pace and finished sixth – almost two minutes behind Leonard Patrick Komon who set a world record.

Helped by ideal cool temperatures and a strong tailwind on the point-to-point course, the lead pack reached the halfway mark on record pace of 1:01:54.

The IAAF rules essentially require marathon records to be established on a loop course (thereby neutralising the impact of wind and course elevation changes).

As part of the 2011 Prefontaine Classic, Mosop was selected in an attempt to break the world record for the infrequently contested 30,000 m on the track.

[15] He was the pre-race favourite and attempted to break the marathon world record, but fell behind Yemane Tsegay and Getu Feleke, eventually finishing with a time of 2:05:03 hours.

[16] Nevertheless, he was selected for the Kenyan Olympic marathon team, but a tendon injury forced him to withdraw and he was replaced by Emmanuel Mutai.