Juan Martin del Potro showed flashes of his best as the Argentine upset Shanghai Masters third seed Alexander Zverev 3-6 7-6 (7-5) 6-4 to reach the quarter-finals.
The 16th-seeded South American beat the 20-year-old Zverev in just under two hours in the pair's first meeting, for his fourth season win in 13 matches against top-10 opponents.
Del Potro, who won the US Open eight years ago over Roger Federer but has struggled for a long time with multiple wrist surgeries and recovery, lost the 2013 Shanghai final to Novak Djokovic in his best performance at the event.
Zverev has already joined Federer and Shanghai top seed Rafael Nadal in the field for next month's ATP Finals in London.
Also on Thursday, Grigor Dimitrov continued to impress as he beat Sam Querrey 6-3 7-6 (7-3).
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The loss prevented Querrey from advancing in the race to reach the eight-player London year-ender.
In other third-round action, Spain's Albert Ramos Vinolas stopped German Jan-Lennard Struff 7-6 (7-4) 6-4.
Nadal and Federer were both due on court later, with the Spanish top seed playing Fabio Fognini of Italy and second seed Federer facing Alexandr Dolgopolov.
