The world number nine fired down 22 aces to subdue Sousa for the third time in as many meetings to claim his first title since August 2014.
The victory maintains the 24-year-old's hopes of claiming a berth at the season ending tournament featuring the world's best eight players.
Novak Djokovic, Roger Federer, Andy Murray and Stan Wawrinka have already qualified for the ATP finals.
(Reporting By Dmitriy Rogovitskiy, editing by Pritha Sarkar)
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