More than twice as many grassroots figures opted for Mr Hughes over Charles Kennedy, the front-runner and hot favourite. The new leader will be crowned on 9 August after a ballot of the party's 90,000 members.
The survey of 152 leading Lib Dem activists suggests the contest may be much closer than previously expected. Mr Hughes was the first choice of 64 members, while Mr Kennedy won 30 votes, Jackie Ballard 24, David Rendel 20 and Malcolm Bruce 14.
The results of the first poll of Lib Dem members will alarm the Kennedy camp. When the contest began, some Kennedy backers hoped their man could win more than 50 per cent of the votes cast, making him the winner under the system of proportional representation used.
Today's survey suggests Mr Hughes enjoys enough support to deny the front- runner a first round win. If that happens, the bottom candidate drops out and his second preference votes are redistributed until one candidate obtains more than 50 per cent of the votes.
Equally worrying for Mr Kennedy is that Mr Hughes also scored well on second preference votes. He was the second choice of 44 members questioned, with Mr Kennedy winning 33, Mr Bruce 25, Ms Ballard 22 and Mr Rendel 14.
This suggests Mr Hughes would have a strong chance of winning in the event of the expected run-off between him and Mr Kennedy. Opponents of Mr Kennedy believe there is a majority against him which will rally behind Mr Hughes.
Sharmian Hopkins, a Lib Dem member in Windsor, said: "The media has it wrong when it says Charles Kennedy is the favourite. You get a very different view from inside the party."
Laurence Brass, Lib Dem chairman in the Hertsmere constituency, said: "I think Simon is head and shoulders above all the other candidates. He has the charisma, experience, the common touch and the depth none of the other candidates do."
Professor Alan Stainer, a consultant to the party, said: "I strongly support Simon Hughes. Charles Kennedy would be good but Simon has charisma and is the soul of the party."
Lorely Burt, a councillor in Dudley, said: "I think Simon Hughes has more passion and charisma in his little finger than Charles Kennedy has in his whole body."
There was some evidence that being a Scot could harm Mr Kennedy's prospects. "After devolution the Welsh and Scots have their own parties, so it would be invidious to have a Celt as leader of the federal party," said David Evans, the campaigns and computer officer in Ceredigion.
Additional reporting: Clarissa Ford and Jonathan ReedReuse content