Seventh place at the 2011 Kenyan trials meant that he was not selected for the world event, but a dispute between Leonard Komon and Athletics Kenya saw Tanui drafted in as a late replacement. He went on to finish the 2011 IAAF World Cross Country Championships as his nation's best performer by taking the silver medal, two seconds behind race winner Imane Merga. Tanui also led the Kenyans to the team gold medal. A third-place finish at the Trofeo Alàsport meet behind Merga and Caleb Ndiku brought his cross country season to a close. He ran a series of track bests that year starting with 10,000 metres run of 26:50.63 minutes for fourth place at the Prefontaine Classic, a time of 13:04.65 min for the 5000 m in Barcelona and then 3000 metres best of 7:50.88 min in Arzana. As one of the fastest Kenyans over 10,000 m that year, he was chosen to compete in that event at the 2011 World Championships in Athletics. However, he ran a minute slower than his season's best in the event final and finished ninth overall.