The Italian rider won the Tour de France.

He also stood on every step of the podium in the Giro d'Italia.

In addition, he won the Mountains Jersey in both races and placed in the World Championship Road Race.

Nencini won the 1960 Tour de France in front of Graziano Battistini of Italy and Jean Adriaenssens of Belgium.

Nencini won the 1957 Giro d’Italia in front of Louison Bobet of France and Ercole Baldini of Italy.

Nencini was also 2nd in the 1960 Giro d'Italia behind Jacques Anquetil of France.

In addition, Nencini was 3rd in the 1955 Giro d'Italia behind Fiorenzo Magni and Fausto Coppi of Italy.

Nencini also won the Mountains Jersey in the 1955 Giro d'Italia.

In the World Championship Road Race, Nencini was 4th in 1955 behind Stan Ockers of Belgium, J-P Schmitz of Luxembourg, and Germain Derycke of Belgium.