SHANGHAI—Plodding progress in trade negotiations between the U.S. and China this week is partly the result of a new tactic from Beijing, which increasingly thinks waiting may produce a more-favorable agreement.

U.S. and Chinese trade negotiators held four hours of talks Wednesday, after a dinner the night before, and then wrapped up their first face-to-face meeting since negotiations foundered more than two months ago. Both sides described the talks as constructive and said the next round will be held in September.

In...