The vote came shortly after Texas Sen. Ted Cruz held the Senate in session overnight — and the Twitterverse in his thrall — with a near-22-hour speech that charmed the tea party wing of the GOP, irritated the leadership and was meant to propel fellow Republican lawmakers into an all-out struggle to extinguish the law.
Defying one's own party leaders is survivable, he declared in pre-dawn remarks on the Senate floor. "Ultimately, it is liberating."
Legislation passed by the Republican-controlled House last week would cancel all funds for the three-year-old law, preventing its full implementation. But Senate Democrats have enough votes to restore the funds, and Majority Leader Harry Reid labeled Cruz's turn in the spotlight "a big waste of time."
Any differences between the two houses' legislation must be reconciled and the bill signed into law by next Tuesday to avert a partial shutdown.
The issue is coming to the forefront in Congress as the Obama administration works to assure a smooth launch for the health care overhaul's final major piece, a season of enrolment beginning Oct. 1 for millions who will seek coverage on so-called insurance exchanges.
Health and Human Secretary Kathleen Sebelius told reporters this week that consumers will have an average of 53 plans to choose from, and her department estimated the average individual premium for a benchmark policy known as the "second-lowest cost silver plan" would range from a low of $192 in Minnesota to a high of $516 in Wyoming. Tax credits will bring down the cost for many.
Republicans counter that the legislation is causing employers to defer hiring new workers, lay off existing ones and reduce the hours of still others to hold down costs as they try to ease the impact of the bill's taxes and other requirements.
"Obamacare is destroying jobs. It is driving up health care costs. It is killing health benefits. It is shattering the economy," said Cruz.
Topsy, a search engine that's a preferred partner of Twitter, calculated on its website during the day that there had been about 200,000 tweets containing the words "Ted Cruz" in the previous day.
Eight months in office, he drew handshakes from several conservative lawmakers as he finished speaking and accolades from tea party and other groups. Chris Chocola, president of the Club for Growth, said Americans owe "Cruz a debt of gratitude for standing on principle in the fight to stop Obamacare."
In addition to the praise, Cruz he drew a withering rebuttal from one fellow Republican, Arizona Sen. John McCain.
McCain read aloud Cruz's comments from Tuesday comparing those who doubt the possibility of eradicating the health care law to former British Prime Minister Neville Chamberlin and others who had suggested Adolf Hitler and the Nazis could not be stopped in the 1940s.
"I resoundingly reject that allegation," said McCain, whose grandfather led U.S. carrier forces in the Pacific during World War II, and whose father commanded two submarines.
"It does a great disservice to those Americans who stood up and said 'what's happening in Europe cannot stand.'"
Even with the 100-0 vote, the legislation faces several hurdles that must be overcome as both houses and lawmakers in both parties work to avoid a partial shutdown next Tuesday.
The struggle over restoring funds for the health care law is by far the most contentious unresolved issue.
Senate Democrats also want to increase funding for federal firefighting efforts without making offsetting cuts to other programs. The House-passed bill provides $636 million for the program, but includes reductions elsewhere to avoid raising the deficit.
To avoid a partial government shutdown, a single, agreed-upon version must be approved by Congress and signed by Obama by Tuesday.
The shutdown issue is a particularly haunting one for Republicans, some of whom were in Congress two decades ago when the GOP suffered politically as the result of a pair of government closures in the winter of 1995-1996.
In a further complication, Treasury Secretary Jacob Lew told Congress that the Treasury's ability to borrow funds will be exhausted on Oct. 17, and legislation is needed to renew its authority if the government is to avoid a first-ever default.
The House is expected to approve a measure later this week allowing Treasury to borrow freely for another year, although that legislation, too, will include a provision to carry out the Republican campaign against "Obamacare." While no final decisions have been made, party officials say a one-year delay is likely to be added, rather than the full-fledged defunding that is part of the spending bill awaiting action in the Senate.
If the events themselves were complicated, the political manoeuvring was no less so.
At least temporarily, they pitted Cruz and his tea party allies inside Congress and out against the party establishment, including House Speaker John Boehner and the Senate GOP leader, Mitch McConnell of Kentucky.
Little more than a week ago, conservatives in the House rank and file forced Boehner and other leaders to include the defunding provision on legislation required to avoid a shutdown, despite their concerns that it would set the party up for failure.
Within hours after the measure cleared the House, Cruz infuriated his allies by virtually conceding he wouldn't have the votes to prevail in the Senate, and stating that "At that point, House Republicans must stand firm, hold their ground and continue to listen to the American people."
Cruz appeared at a news conference the next day to proclaim he would do "everything and anything possible to defund Obamacare," including a possible filibuster of legislation to prevent a shutdown.
Senate Republicans were less than enthusiastic about that, and several said so and made it clear they would not follow the path that Cruz laid out of seizing every opportunity to slow or stop the bill. By Tuesday, the Texan was under pressure from fellow Senate Republicans to let the legislation pass relatively quickly, to make sure the government stayed open.
When he began his remarks, he vowed to speak in opposition until "I am no longer able to stand."
Nearly 24 hours later, he offered to shorten the time it would take to debate the measure and voted along with Republicans and Democrats alike to send it over its first hurdle.
Associated Press writers Donna Cassata, Andrew Taylor and Stephen Ohlemacher and Social Media Editor Eric Carvin contributed to this story.