A new poll shows Mitt Romney flipping a 5-point deficit in Colorado before the first presidential debate, which was held on Wednesday in Denver, to a 3.5-point advantage later in the week — another signal that Mr. Romney’s comparatively strong debate performance has started to translate into rising poll numbers for the Republican.

A poll from Gravis Marketing, conducted Oct. 3-4, shows Mr. Romney with a 49.4 percent to 45.9 percent lead over Mr. Obama. The president had held nearly a 5-point lead in a poll conducted Sept. 25, at 50.2 percent to 45.5 percent.

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Mr. Obama’s job approval numbers are also significantly underwater in the new poll: 40.5 percent approve, while 50.9 percent disapprove. Just 36.8 percent of voters say the country is on the right track, compared to 53.5 percent who think it’s on the wrong track.

The political party affiliation of the survey’s sample was about 32 percent Republican, 28 percent Democrat and 40 percent “other.”

The poll surveyed 1,438 likely voters on Oct. 3-4, and 1,285 gave a response on their preference for president. The margin of error of the poll is 2.8 percentage points.

Elsewhere, a new national poll from Clarus Research Group also shows Mr. Romney taking a slight lead among voters nationwide after trailing Mr. Obama earlier in the week. Mr. Obama led by 4 points in a poll conducted Tuesday, but Mr. Romney leads by 1 point in a poll conducted Thursday — the day after the debate.

The polls of 590 likely voters have a margin of error of about 4 percentage points.