Pablo Andujar suffered a straight-sets defeat to Jiri Vesely on his return from a lengthy injury lay-off at the Shenzhen Open.
Andujar made his comeback on Tuesday, having been sidelined since March with an elbow problem that required surgery.
The Spaniard was unable to get the better of eighth seed Vesely, who prevailed 6-2 7-6 (10-8) in his first match since an arm injury forced him to withdraw from a second-round meeting with Novak Djokovic at the US Open earlier this month.
Vesely was one of two seeds in action in Shenzhen, with Benoit Paire also progressing courtesy of a three-set triumph over Nikoloz Basilashvili.
Tuesday's other first-round winners were Thomaz Bellucci, Inigo Cervantes, Ryan Harrison, Malek Jaziri, Janko Tipsarevic and Mikhail Kukushkin, who ousted Lukas Rosol in a third-set tie-break to set up a meeting with top seed and defending champion Tomas Berdych.
Rain brought a premature end to proceedings in the other ATP 250 event being held in China this week, the Chengdu Open.
Seventh seed Joao Sousa suffered a 7-6 (7-3) 6-3 loss to Karen Khachanov prior to play being suspended, while there were victories for Paolo Lorenzi, Kevin Anderson, Dusan Lajovic, Lu Yen-hsun and Adrian Mannarino.
Three matches will resume on Wednesday having been interrupted, including a contest between Marcos Baghdatis and Pablo Carreno Busta that is tied at 5-5 in the final set.