Austrian fourth seed Thiem, a US Open quarter-finalist last year who also went out at the first hurdle at Wimbledon, was beaten by the same player who dispatched Greek sixth seed Stefanos Tsitsipas in the first round at Wimbledon.
Fabbiano next plays Alexander Bublik of Kazakhstan in a draw quarter that is suddenly wide open after the exit of its three top-ranked players, Thiem and rising star Tsitsipas, who fell to Russian Andrey Rublev, plus Spanish 10th seed Roberto Bautista Agut, who lost in five sets to Kazakhstan's Mikhail Kukushkin.
Nadal rampant at US Open as Thiem, Tsitsipas lead exodus
The top seed remaining in the quarter is France's 13th-seeded Gael Monfils.
Spanish second seed Rafael Nadal's path to the US Open crown became much easier with the ouster of the three top-10 rivals.
The only top-10 rivals remaining in Nadal's half of the draw as he chases a 19th Grand Slam title are still in his quarter of the draw, however, in German sixth seed Alexander Zverev and Russian ninth seed Karen Khachanov.
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