Pablo Cuevas was the only seed in action at the Shanghai Masters on Sunday, but became the first major casualty of the tournament as he lost to wildcard Wu Di in the first round.
That shock result came at the end of a day of upsets, as Albert Ramos-Vinolas and Philipp Kohlschreiber also fell to lower-ranked opponents.
World number 41 Kevin Anderson, though, made a solid start to his campaign, beating China's Li Zhe 6-1 6-3 to set up a second-round clash with sixth seed Gael Monfils.
As 16th seed, Cuevas should have been looking to lay down a marker on a day of limited first-round action in Shanghai.
However, the Uruguayan was dumped out by world number 184 Wu, who delighted the home crowd with an unlikely 6-3 4-6 7-6 (7-2) triumph.
Despite his instant response to Wu's first break of serve in the opening set, Cuevas was unable to bounce back from the second, falling to his opponent's fifth set point.
Cuevas broke at 5-4 to snatch the second set before the decider saw just two games go with serve, and the South American's struggles carried into the tie-break.
TIPSAREVIC MAKING PROGRESS
Janko Tipsarevic has been on the comeback trail over the past couple of seasons following a foot injury that kept him sidelined for 17 months.
And the Serbian has been in fine form of late, reaching the semi-finals of the Shenzhen Open this month before being forced to retire during the second set of that match.
But Tipsarevic - ranked 173rd in the world - looks intent on building a strong run and beat world number 31 Kohlschreiber 6-2 6-4 on Sunday.
Ramos-Vinolas was beaten 7-5 6-3 by Fabio Fognini, whose reward is a second-round clash with Novak Djokovic.