A stunning 24-hour span saw May on Tuesday dealt the heaviest drubbing by parliament in modern British political history - 432 votes to 202 - over the divorce terms she reached with Brussels.
She emerged victorious in parliament's first no-confidence vote in a British government in 26 years on Wednesday by a 325-306 margin, a majority of 19.
But it may have only been a pyrrhic victory for the hobbled but determined premier as she tries to steer the world's fifth-biggest economy through its biggest crisis in a generation.
The opposition Labour Party could try to oust her government again in the hope of triggering snap elections before Britain's scheduled March 29 Brexit date.
And May herself is working on the tightest-possible deadline as Britain prepares to leave the bloc that for half a century defined its economic and political relations with the rest of the world.
She has promised to return to parliament on Monday with an alternative Brexit strategy devised through cross-party talks with the opposition.
There is now an assumption among many European diplomats that Brexit will have to be delayed to avoid a potentially catastrophic "no-deal" breakup.
May notably refused to rule out the idea when quizzed about it in parliament earlier on Wednesday.
Before Tuesday's vote, EU leaders repeatedly said they will not reopen the withdrawal deal sealed at a special Brussels summit in December.
But, following the defeat, French President Emmanuel Macron suggested there may be room to "make improvements on one or two things."
German Chancellor Angela Merkel added: "We still have time to negotiate but we're now waiting on what the prime minister proposes."
Irish Prime Leo Varadkar added: "We have always said that if the United Kingdom were to evolve from its red lines on the customs union and on the single market, that the European Union could evolve also."
More than one third of May's MPs - 118 out of 317 - voted against her Brexit deal, and Labour leader Jeremy Corbyn said she was leading a "zombie government".
Opening the no confidence debate on Wednesday, he said the agreement was "officially dead" and demanded May "do the right thing and resign".
But the prime minister, who stood up to speak to cheers from her own side, said an election was "the worst thing we could do".
"It would deepen division when we need unity, it would bring chaos when we need certainty and it would bring delay when we need to move forward," she said.
However, the vote left Britain with no plan as it prepares to leave the bloc that for half a century has defined its economic and political relations with the rest of the world.
While MPs agreed to reject May's deal, they had different reasons, with some judging that it either kept Britain too close to the EU or not close enough.
And there was still no consensus on how to proceed.
Many Brexit supporters, including Northern Ireland's Democratic Unionist Party (DUP), which props up May's government in parliament, want her to renegotiate her deal.
But for pro-Europeans, Tuesday's vote fired the starting whistle on a more radical bid to change her strategy.
Dozens of MPs are calling for a second referendum with an option to cancel Brexit altogether.
Scottish First Minister Nicola Sturgeon said it was the "only credible option", adding: "We don't have any more time to waste."