General classification contenders Vincenzo Nibali and Sergio Higuita finished safely in the front group, in a rainy and windy stage.
Nizzolo takes first win for team under leadership of Riis, Impey sets up final-stage showdown with Porte.
Giacomo Nizzolo signs with Dimension Data and Laurens ten Dam is set to join BMC-CCC, as Hugh Carthy renews with EF Education First-Drapac
Nizzolo's 2017 season was essentially a wash due to injury and health problems. This year, he's got his first win and a bit of confidence.
Giacomo Nizzolo won the final stage of the 2018 Vuelta a San Juan on Sunday in the host city, as Gonzalo Najar captured the overall title.
The 27-year-old Italian is a strong sprinter and classics rider.