Nigeria international Troost-Ekong made his sixth appearance for the White and Blacks and played for the duration of the game.
The 26-year-old defender played a key role for his side as the first half ended without conceding, frustrating the attacks of Vincenzo Montella‘s men.
In the 72nd minute, however, Nikola Milenkovic broke the deadlock, heading home Erick Pulgar’s cross.
The effort from the Serbian made the difference in the encounter as Udinese left Stadio Artemio Franchi without a point.
Algeria international Rachid Ghezzal was introduced into the game with three minutes left to play for Franck Ribery.
The 27-year-old winger has now made two appearances for the Purple One since his summer loan move from Premier League club Leicester City.
With the result, Udinese dropped to 14th place in the log with seven points from seven games while Fiorentina climbed to the fifth spot with 11 points from the same numbers of games.
Troost-Ekong will hope to help his side return to winning ways after the international break, as he is expected to lead the Super Eagles against South American giants Brazil in an international friendly on October 13.