Theresa May will travel to a critical European Union summit with her authority diminished after Tory rebels inflicted a humiliating House of Commons defeat on the Government in a major Brexit vote.
MPs proclaimed Parliament had "taken back control" of the Brexit process after they defeated the Government to ensure a "meaningful vote" on the withdrawal deal.
The Prime Minister will hope it does not damage the confidence of EU leaders in her authority to conduct Brexit negotiations as they prepare to rubber-stamp a move forward to trade talks.
In a night of high drama, rebel ringleader Dominic Grieve told the Government it was "too late" as ministers made last-minute concessions in an attempt to head off the revolt.
He saw his amendment to the EU (Withdrawal) Bill squeezed through the Commons on a majority of four amid tense scenes.
It means MPs and peers will be given more control over the Government's implementation of the withdrawal agreement, as ministers will have to pass a statute, which can be amended, before it takes effect.
Mrs May who attempted to reassert authority by sacking Tory vice chair and Brexit rebel Stephen Hammond, could face questions about the vote's implications at a dinner with the other 27 EU leaders on Thursday, who she will urge to begin trade talks as quickly as possible.
The European Commission's assessment that "sufficient progress" has been made on divorce issues to move Brexit negotiations on to their second phase gave the PM a huge boost just last week.
And the EU27 are expected to green-light phase two when they meet in Mrs May's absence on the second day of their two-day summit in Brussels on Friday.
But the political capital she has built up was dealt a damaging blow by Thursday's vote, which led to bitter recriminations in the Conservative Party, with 11 MPs joining opposition parties in backing the amendment, and a handful of others abstaining.
The European Parliament's chief Brexit co-ordinator Guy Verhofstadt tweeted: "British Parliament takes back control. European and British Parliament together will decide on the final agreement. Interests of the citizens will prevail over narrow party politics. A good day for democracy."
Backers of a "soft" Brexit, including Tory rebels Nicky Morgan and Anna Soubry, also hailed the result.
Ms Morgan tweeted: "Tonight Parliament took control of the EU Withdrawal process".
Labour leader Jeremy Corbyn, who will be cheered by the fact that only two of his own Brexiteer MPs rebelled to back the Government, said: "This defeat is a humiliating loss of authority for the Government on the eve of the European Council meeting.
"Theresa May has resisted democratic accountability. Her refusal to listen means she will now have to accept Parliament taking back control."
Mr Grieve said he had no option but to push his amendment to a vote because the Bill gave "intransigent" ministers "the biggest Henry VIII power ever conferred on Government" with no justification.
The former attorney general evoked Winston Churchill during the debate, telling the Commons: "There's a time for everybody to stand up and be counted" and stressing he put "the country before the party".
He said his amendment would not stop Brexit but the vote provoked a furious backlash from Leavers.
Tory Nadine Dorries called for the deselection of rebel Tories for "undermining the PM", while accusing Mr Grieve of "treachery".
But rebel Tory Sarah Wollaston hit back on Twitter, saying: "Get over yourself Nadine."
Downing Street said it would "respect the will of MPs" but a Government spokeswoman suggested it may seek to amend the Bill during later stages of its passage through Parliament.