Hillary Clinton. AP Right off the bat on Thursday night, Hillary Clinton attacked US Sen. Bernie Sanders (I-Vermont) during their first one-on-one debate of the presidential race.

Clinton first took shots at Sanders at the debate's opening, saying that the senator was wrong to promise changes that had little chance of passing through Congress.

"I am not making promises that I cannot keep," Clinton said in her opening statement at the Durham, New Hampshire, debate.

Clinton reiterated that she opposed several of Sanders' plans, including one to replace the Affordable Care Act and his plan to make colleges tuition-free.

"We have a difference. I believe in affordable college, but I don't believe in free college," Clinton said. "I believe that middle-class kids, not just Donald Trump's kids, get to afford college."

She added:

The numbers just don't add up from what Sen. Sanders has been proposing. That's why all of the independent experts, all of the editorial boards that have vetted both of us have concluded that it is just not achievable. Let's go down a path where we tell people what we actually will do. A progressive is someone who makes progress.

Clinton later took a jab at Sanders' definition of progressive values.

She noted that US President Barack Obama has also taken donations from Wall Street, as her campaign has. She noted that US Vice President Joe Biden supported the Keystone XL Pipeline, as Sanders has blasted her for doing. And she noted that local Sen. Jeanne Shaheen (D-New Hampshire) supported the Pacific trade pact over which Sanders has also criticized her.

"Who's left in the progressive wing of the Democratic Party?" she asked.

For his part, Sanders emphasized that though he respects Clinton, he disagreed with Clinton's healthcare and higher-education plans.

"I do not accept that belief that the United States of America and our government can't stand up to the rip-offs of the pharmaceutical industry," he said.

Colin Campbell contributed reporting.