Instant-reaction polls conducted by CNN and CBS News suggest that Mitt Romney was the winner of the first presidential debate.

A CNN poll of debate-watchers found Mr. Romney very clearly ahead, with 67 percent of registered voters saying he won the debate, against just 25 percent for President Obama.

A CBS News poll of undecided voters who watched the debate found 46 percent siding with Mr. Romney, 22 percent for Mr. Obama and 32 percent saying it was a tie.

Google, which is experimenting with online surveys, found 38.9 percent of respondents saying they thought Mr. Obama performed better in a poll it conducted during the debate, against 35.5 percent for Mr. Romney and 25.6 percent who said it was a draw. But a second poll they conducted after the debate found 47.8 percent of respondents giving Mr. Romney the advantage, against 25.4 percent for Mr. Obama.

There is not a lot of empirical research on the relationship between instant reaction polls and their eventual effect on the head-to-head polls. However, these were strong numbers for Mr. Romney where comparisons to past post-debate polls are available. A similar CBS News poll conducted among undecided voters after the first debate in 2008, for example, found that 40 percent said that Mr. Obama won the debate, against 22 percent for John McCain. The head-to-head polls moved toward Mr. Obama by about three percentage points after that debate, although some of that may have been from the momentum that Mr. Obama had carrying into the evening.

The 67 percent of voters in the CNN poll who said that Mr. Romney won Wednesday night’s debate was higher than in any of the network’s surveys of the 2008 debates.

By comparison, 51 percent of debate-watchers in a CNN poll after the first presidential debate in 2008 said that Mr. Obama had the stronger performance. And 58 percent said so after the third and final presidential debate in 2008.

There may be some mitigating factors for Mr. Obama. First, although the conventional wisdom was that Mr. Obama had a lackluster performance throughout most of the debate — he certainly had an extremely cautious and defensive strategy — there were few obvious moments in which he said things that will make for compelling YouTube clips or cable news soundbites.

Second, head-to-head polls throughout the election cycle have been hard to influence for any reason. There are few undecided voters remaining — and undecided voters may be less likely than others to have actually watched the debates.

Still, it seems likely that Mr. Romney will make at least some gains in head-to-head polls after the debate, and entirely plausible that they will be toward the high end of the historical range, in which polls moved by about three percentage points toward the candidate who was thought to have the stronger debate.

The FiveThirtyEight “now-cast” — our estimate of what would happen in an election held immediately — had Mr. Romney trailing by a wider margin than three points in advance of the debate. (Instead, it put his deficit at about five points nationwide.) But our Nov. 6 forecast anticipated that the race would tighten some. It’s going to take a few days for any reaction to the debate to filter through the FiveThirtyEight model.

My own instant reaction is that Mr. Romney may have done the equivalent of kicking a field goal, perhaps not bringing the race to a draw, but setting himself up in such a way that his comeback chances have improved by a material amount. The news cycle will be busy between now and Nov. 6, with a jobs report coming out on Friday, a vice-presidential debate next week and then two more presidential debates on Oct. 16 and Oct. 22.

According to one prominent offshore gambling site, Pinnacle Sports, Mr. Obama’s odds of winning the election declined to about 73 percent after the debate from around 80 percent beforehand.