Gwinn's powerful 66th-minute shot from the edge of the penalty area flew into the left corner. The ball fell to her after Chinese defenders failed to properly clear a corner floated in from the right.
In an even first half at Roazhon Park, in the Brittany city of Rennes, Germany defender Carolin Simon hit the crossbar and China striker Yang Li hit the post. China failed to take advantage of pressure they created in the second half.
Germany won their last title in 2007 and next face Spain in Group B on Thursday, while China, runners-up to the United States in 1999, play South Africa on Friday.
In yesterday's third game, Guro Reiten and Lisa Marie Utland scored to help Norway open the tournament with a 3-0 victory over Nigeria.
The 1995 winners played without Ada Hegerberg, the 2018 Fifa Ballon d'Or winner who stepped down from the national team because of what she says are differences in the way the Norwegian federation treats the men's and women's teams.
Reiten's deflected shot in the 17th minute gave Norway the lead, and Utland scored in the 34th minute. An own goal made it 3-0 and wrapped up scoring before the break.
Nigeria were hurt when defender Faith Michael was stretchered off after a collision with her keeper early in the second half.
New Zealand start their tournament with a match against the Netherlands on Wednesday at 1am.
- AP