WASHINGTON – Describing Republican presidential nominee Mitt Romney’s debate performance as “terrific,’’ Sen. Rob Portman said “the persuadable voters are now going to listen’’ more carefully to Romney’s message.

Portman, R-Ohio, who played President Barack Obama against Romney in the debate preparations, said Romney “talked about what people wanted to hear’’ in the Wednesday debate in Denver.

“It may not show up in the polls immediately, but it’s opened the door for Romney to reach through to these people, and in the end they might give him a chance,’’ Portman said yesterday. “We have a lot of voters who are persuadable.’’

Portman said that most undecided voters know what to expect from the president, which meant Romney had a good chance to impress those same voters by showing that “he had a plan.”

“They could hear not only how bad things are, but how they can get better,” said Portman.

Portman, who watched the debate backstage with Romney’s aides in Denver, said Obama appeared “uncomfortable,’’ which did not surprise the Ohio senator. Portman said Obama rarely gets “asked any questions; that’s probably why he was uncomfortable.’’

Portman declined to take credit for Romney’s performance, saying that “he did well, not because of the prep, but because he was confident.”

Portman said Romney was particularly effective with undecided voters in Ohio. He said that “Ohio has been the No. 1 state for the negative ads against Mitt Romney. That was one of the benefits of having a face-to-face discussion without the media filter.’’