Hilary Benn and Alan Johnson were neck and neck in the race to replace John Prescott as the second round of nominations closed today.
The international secretary consolidated his lead position among grassroots members with 77 constituency Labour party branches nominating him for the deputy leadership post, while just 45 backed Mr Johnson.
The result reverses the outcome of the first round of nominations by fellow Labour MPs, which saw the education secretary top the poll (73), while Mr Benn struggled over the threshold of nominations needed to enter the race by just two votes (47).
The 352 Labour MPs eligible to take part will have a weighted vote alongside 19 Labour MEPs in a three-way electoral college. The other two segments are Labour party members and Labour affiliated trade unionists.
Mr Benn is now the bookies' favourite to win the contest, with Mr Johnson in second place.
Mr Benn's campaign chair, Ian McCartney, said today's result showed the international secretary was a "grassroots politician".
He said: "Labour party members are flocking to his campaign but there is a long way still to go. I am calling on rank and file trade unionists like myself to join our campaign and to back Hilary's call for a fairer deal for hardworking men and women."
Jon Cruddas, the backbench MP for Dagenham who is seen as the most left-wing candidate on the slate, boosted his support after a Newsnight hustings appearance earlier this week. He ranks second in popularity among Labour party members, with 68 pledging their support.
Backing for the other three candidates was as follows:
Justice Minister Harriet Harman (60), Labour party chair Hazel Blears (36) and northern Ireland secretary Peter Hain (23).
The six will take part in a hustings in Scotland tomorrow and at the GMB conference on Monday.
The GMB is the third largest affiliated trade union and the only one not to have declared its chosen candidate.
The new super-union Unite (formerly Amicus and the T&G) has backed Jon Cruddas, while Unison is supporting Alan Johnson.
