Labour left-wingers were celebrating on Friday night after they won the lion's share of seats in elections to the party's ruling body.
A Momentum-backed slate of candidates won seven posts on the Labour National Executive Committee, making them the largest faction in the contest.
But the victory is unlikely to be enough to cause serious trouble for Keir Starmer, who retains a working majority on the NEC – partly because it is only partially elected by members.
A new proportional voting system also ensured more representation for the party's right wing or moderates, whose Labour To Win slate of candidates picked up three seats. They have pledged to support the leadership.
But it was a disappointing night for the "soft-left" Open Labour faction, who had hoped to build on Sir Kier's victory in this year's leadership contest. Just one of their candidates, independent-minded NEC veteran Ann Black, was elected.
The victory of the three candidates from the party's right means the Labour leader has a larger majority on the NEC than before, when all elected seats were held by the left.
But the change of voting system made this all but inevitable, and the strong performance by the left makes Sir Keir's majority potentially vulnerable to future changes in leadership at trade unions, who pick a large number of the seats on the NEC.
The leadership of unions like like Unison and GMB generally support Sir Keir, but have general secretary elections coming up which could change the calculation on the Labour ruling body.
Left-wingers said their voters were galvanised by opposition to Jeremy Corbyn's suspension, and early signs that Keir Starmer would lead the party from a less left-wing position than he had campaigned on in the leadership election.
Speaking after the result, Andrew Scattergood, Momentum co-chair, said: “Members have decisively rejected the anti-democratic crackdown implemented over the last few weeks by a factional group around the leadership.
“Keir Starmer has shown worrying signs of breaking with the values of party unity and socialist policy on which he was elected — this result should warn against that course of action."
Luke Akehurst, a newly elected NEC member from the party's right, aped Tony Blair, tweeting: "A new dawn has broken, has it not?"
Join our commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies