President Obama announced the nomination of Sylvia Mathews Burwell to become the new secretary of the Health and Human Services Department on Friday and said goodbye to departing Secretary Kathleen Sebelius, who he said will "go down in history" for her work in expanding access to health insurance.

Sebelius led the sprawling department "when the United States of America finally declared that quality, affordable health care is not a privilege but it is a right for every single citizen," Obama said at an event in the White House Rose Garden.

The president readily acknowledged that Sebelius' role over the tumultuous five years after the passage of the bill and its rocky implementation did not come without costs.

"Kathleen has been here through the long fight to pass the Affordable Care Act. She's got bumps, I've got bumps, bruises," he said, quickly referencing the glitch-filled rollout and the months of public relations fallout.

“Yes, we lost the first quarter of [the] open enrollment period with the problems with, and there were problems,” he said.

But in the end, Obama added, Sebelius and her staff exceeded the administration's goal for enrolling 7 million in the law's insurance exchanges by the March 31 deadline.

She and her staff "turned the corner, got the job done. And the final score speaks for itself," he said, of the 7.5 million Obamacare sign-ups.

The crowd, filled with supportive cabinet secretaries and administration officials, gave Sebelius several standing ovations and applause as Obama cited her accomplishments.

Standing next to Obama in a tailored grey suit, she was mostly stoic during the event, but when Obama threw out the 7.5 million enrollment figure, she smiled broadly as the crowd rose to its feet.

Sebelius said her time as HHS secretary has been "the most meaningful work I've ever been a part of. In fact, it has been the cause of my life.”

“We are on the front lines of a long overdue national change, fixing a broken health system,” she said.

“I knew it wouldn't be easy... but throughout the legislative battles, the Supreme Court challenge, a contentious re-election and years of votes to turn back the clock, we are making progress, tremendous progress. And critics and supporters alike are benefiting from his law,” she added.

Sebelius got some chuckles from the crowd when she noted a page was missing from her prepared remarks, and quickly wrapped up.

Turning to Burwell's ascension to the top spot at HHS, Obama said he "could choose no manager more experienced, more competent."

Burwell, 48, a former Clinton administration official who has served one year as the director of the Office of Management and Budget, "is a proven manager” who knows how to get results, he said, referring to the “tough tasks, big challenges” that lie ahead for the health care law.

“I hope the Senate confirms Sylvia without delay,” he said. “Last time, she was confirmed unanimously. I'm assuming not that much has changed since the last time.”

The Senate confirmed Burwell as Obama's budget director on a 96-0 Senate vote nearly a year ago. Her nomination is all but guaranteed under a rule change put in place late last year by Senate Majority Leader Harry Reid, D-Nev., that allows a straight majority vote on all presidential nominations.

The Harvard-educated West Virginia native who served as deputy White House chief of staff and deputy to the Treasury secretary in the Clinton administration, has “demonstrated her ability to field great teams, forge strong relationships and deliver excellent results at the highest levels, and she's done it both in the public and private sector.”

After the Clinton administration, she left D.C. for Washington state, where she was the head of the Bill and Melinda Gates Foundation, later joined the Walmart Foundation and served on Metlife's board of directors.

Obama half-jokingly gave his budget director credit for helping bring down the deficit over the last year.

“In the year since she arrived, the deficit has plunged by more than $400 million,” he said, adding, “I'm just saying — that's happened during that time.”

Obama also gave her credit for exuding a calm leadership presence during the government shutdown last October when most of her staff were barred from reporting to work, and said she was “vital” in forging the two-year budget agreement with Republicans.

“Sylvia was a rock, a steady hand on the wheel who helped navigate the country through a very challenging time,” he said.

In very brief remarks, Burwell thanked Obama for the tremendous confidence he had placed in her.

“I'm humbled, honored and excited by the opportunity to build on the achievements that Kathleen, the president and so many others have put in place,” she said.

Burwell's ability to rise above the blistering partisan fray will be tested immediately as she attempts to persuade a skeptical public that Obamacare is on a smoother path and won't create more uncertainty and chaos for patients, doctors, hospitals and insurers alike.

Burwell will be forced to confront an onslaught of questions about the law's future from Republicans, as well as Democrats angered over the disastrous rollout's impact on their reelection chances.

Americans want to know how many enrollees have actually paid their premiums, whether more people will lose the plans they had and whether premiums and deductibles will continue to shoot up in the months ahead.

Although they cannot block her confirmation, Senate Republicans are already promising to put Burwell through the paces.

“She inherits a very, very difficult task and she's going to have a tough road ahead of her in terms of securing the Senate confirmation, especially if she is not prepared to answer all kinds of questions about how independent she's willing to be and how open and transparent she's willing to be with Congress," Sen. Mike Lee, R-Utah, a conservative stalwart who pushed hard to defund Obamacare last year, told Fox News' Greta Van Susteren on Thursday night.

Even in the post-nuclear Senate, Lee predicted Burwell will face a serious grilling from both Republicans and Democrats who are taking the heat for the law's rocky beginning.

Senate Minority Leader Mitch McConnell, R-Ky., said he hopes Burwell's nomination is the start of "a candid conversation about Obamacare's shortcomings and the need to protect Medicare for today's seniors, their children and their grandchildren."

This story was published at 11:36 a.m. and has been updated.