Barack Obama used an unusually lengthy and informal desert summit to present Chinese president Xi Jingping with detailed evidence of intellectual property theft emanating from his country.
Meanwhile, a top US official declared cyber-security was now at the "centre of the relationship" between the world's largest economies.
While there were few clear policy breakthroughs on cyber-security, US officials said President Obama and Mr Xi were in broad agreement over the need for North Korea to be denuclearised. And both countries expressed optimism that the closer personal ties forged between the two leaders during the California summit could stem the mistrust between the world powers.
However, Mr Obama's national security adviser Tom Donilon said resolving cyber-security issues would be "key to the future" of the relationship. Mr Obama told Mr Xi that "if it's not addressed, if it continues to be this direct theft of United States property, that this was going to be very difficult problem in the economic relationship and was going to be an inhibitor to the relationship really reaching its full potential" Mr Donilon told reporters after the summit.
In their own recap of the meetings, Chinese officials said Mr Xi opposed all forms of cyber-spying, but claimed no responsibility for attacks against the US. "Cyber-security should not become the root cause of mutual suspicion and frictions between our two countries. Rather, it should be a new bright spot in our co-operation," said Yang Jiechi, Mr Xi's senior foreign policy adviser.
Mr Yang said the two leaders "blazed a new trail" away from their past differences at the summit and "talked about co-operation and did not shy away from differences". "The two presidents agreed to build a new model of major country relationship between China and the United States based on mutual respect and win-win co-operation," Mr Yang said. "We have to stay each other's partners, not rivals."
The US president told reporters that the talks were "terrific" as he and Mr Xi walked side by side, both having ditched jackets and ties in a nod to the summit's informal atmosphere. The leaders closed the summit in low-key style, with no formal statements to the press, just a private tea with Mr Xi's wife.
Mr Obama and Mr Xi did take a significant step towards tackling climate change, announcing that their countries had agreed for the first time to partner on reducing hydrofluorocarbons, a potent greenhouse gas used in refrigerators, air conditioners, and industrial applications.
US officials are hoping that Mr Xi, who took office in March, proves to be a new brand of Chinese leader. He has deeper ties to the US than his predecessors, given that he lived in Iowa briefly as a visiting official and sent his daughter to college in the US.
The two leaders appear to have more in common than Mr Obama had with former Chinese leader Hu Jintao, who often appeared stiff and formal in meetings. Both men are in their 50s and share a love of sports - swimming and football on Mr Xi's side, basketball and golf on Mr Obama's. Both are also married to glamorous, high-profile wives who have played a strong role in shaping their images.