The Green Party has pulled out of the Ealing Central and Acton seat in a bid to help Labour beat the Tories.
The move is the first tactical withdrawal of its kind in the country for the 2017 general election, reports Mirror Online .
Labour MP Rupa Huq beat the Conservatives by 274 votes in 2015, but no other party managed more than 7% of the vote.
That prompted the local Green party, which previously won 1,841 votes, to withdraw this time to give Ms Huq more of a chance.
Green Party national leaders want a "progressive alliance" that could stop the Tories taking overall power on June 8, even if they win the most seats.
Jeremy Corbyn has ruled out a formal coalition in Westminster, but did not block informal arrangements like that in west London.
Ealing's local Green members voted on Thursday not to field a candidate after Ms Huq promised to campaign for voting reform and the environment.
The Labour MP will also campaign against Hard Brexit and a Heathrow third runway.
She told the Mirror: "The local Green Party knows that I am an MP who is a resolute Remainer and that, if necessary, I will continue to fight for the UK to stay in the EU and vote accordingly.
"In these perilous times it is vital that we work together to oppose this reckless surge towards Brexit .
"We must adopt a pragmatic approach to avert the existential threat that an invigorated Conservative government would pose to this country.
"The NHS, our invaluable public services and our environmental protections are in crisis. Unfortunately the local Liberal Democrats are prioritising party politics over fighting the Tories.
"I have a majority of 274 and there is a real risk the split of the progressive vote will leave the people of Ealing and Acton with a hard-Brexiteer MP - something they categorically did not vote for on the 23rd of June.
"I have always got on well with my local Greens. We did a number of hustings meetings together in 2015 and have shared common ground on key areas.
"That is why I welcome the Green Party offer of support to take the fight to the Tories. We can only hope in time that the Liberal Democrats see sense and do the same."
A Green Party spokesman said any decision is up to local members.
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