Team USA was the last of 16 clubs entered in the tournament to make an appearance and the Americans fell behind early while being outhit 9-8.
The United States has games remaining against Italy and Canada in the round-robin portion of the tournament and a loss in either of them would likely mean elimination from title contention.
Mexico took a 4-0 lead through three innings and relied on solid pitching the rest of the way. The Mexicans lost their opening game in Pool D to Italy, which has a 2-0 record and has all but wrapped up a spot in the second round of the tournament.
The top two teams from the pool move on to the double-elimination phase of the event that will decide the semifinalists.
Mexico put runners on second and third in the opening inning, after which Luis Cruz produced a run on a sacrifice fly and Gonzalez delivered another with a ground out.
Gonzalez blasted a two-run homer in the third. All four of the early runs were charged to R.A. Dickey.