The CNN/ORC International Poll found 48 percent of the debate watchers surveyed thought the Democratic incumbent won and 40 percent gave the nod to his Republican challenger. That 8-point difference was within the survey's plus or minus 4.5 percentage-point margin of error, CNN said.
The poll found 59 percent thought Obama's performance was stronger than expected, 15 percent thought it was weaker and 23 percent said he met their expectations.
Forty-four percent said Romney did better than expected, while 26 percent graded him as worse than expected and 26 percent said he performed up to their expectations.
The number of people who took part in the snap poll was not provided.
Romney was seen as the winner of the first debate and Obama was ahead in the second debate, though those snap poll results also were within the margin of error.