There were still painting parts of the stadium the morning of the first game at Shea. The stadium was ready to hold a capacity crowd. It was suppose to open in 1963. Construction issues pushed that back to 1964.
Well the that first day had some glitched. Just check out the misspell on the scoreboard in the pic to the right.
The Mets lost to the Pirates that day 4-3. The 50,000 fans that came to opening day were marveled by the new stadium. Of course they could not do anything about the lousy team that was on the field.
Also check out the scorecard for the first game.