China's top-ranked player Zhang Ze fell at the first hurdle of the ATP event in Beijing, going down 7-6 (4) 6-4 to Bernard Tomic.
The Australian No 1 clawed his way back into the match after being 5-3 down in the opening set to force it to a tiebreaker, which he eventually won.
Zhang, who is 190th in the world rankings, was then broken early in the second set by the 20-year-old Tomic, who went on to seal a second round date with fifth-seeded Frenchman Richard Gasquet.
"We were playing juniors matches before and when Tomic was a junior he was sometimes sloppy and he gave many free points," the 23-year-old Zhang said.
"Now he has grown a lot and he is more serious on every single point when he plays."
In the day's other matches, Tomic's countryman Lleyton Hewitt beat seventh seed and fellow veteran Tommy Haas 7-6 (8-6) 6-3.
Germany's Philipp Kohlschreiber beat Albert Montanes 7-5 1-6 7-6 (7/4) to set up a possible second-round meeting with Rafael Nadal while Grigor Dimitrov suffered a shock 6-4 6-2 exit to Roberto Bautista Agut.
Italy's Fabio Fognini came through in a deciding set against Tommy Robredo from Spain 7-5 4-6 6-3.
Inglot and Huey through
Meanwhile, Great Britain's Dominic Inglot and his partner Treat Huey reached the second round of the men's doubles at the Rakuten Japan Open with victory over Kevin Anderson and Paul Hanley.
The South African-Australian pairing won the first set 6-2 but Inglot and Huey, from the Philippines, came back with a late break of serve in the second set to level the match.
That set up a champions' tie-break and Inglot and Huey prevailed to win the match 2-6 7-5 10-4 in an hour and 10 minutes.