Liberal democrat Dr Evan Harris has held on to his Oxford West and Abingdon seat - with a significantly increased majority.
Conservative candidate Ed Matts was forced to admit defeat after winning 15,485 votes, compared to Dr Harris's 24,670.
Evan Harris Labour's Gillian Kirk, who came in third with 9,114, suggests she was the victim of tactical voting, with some Labour supporters switching to Dr Harris to ensure Mr Matts lost.
The Lib Dem majority was 9,185, up from 6,285 in 1997.
After the count was declared at 3.30am in the sports centre at Radley College, Dr Harris said: "Labour has not delivered on many promises and failed to meet people's expectations.
"They followed previous Tory policies and that is why the Liberal Democrats came through.
"I hope the new Labour Government will listen to the people and take the challenge to be radical, investing in additional resources for all our services and reforming the way local government is funded."
Since Dr Harris snatched the traditional Tory seat four years ago, he has nursed the sprawling constituency, which stretches from Kidlington in the north, through west Oxford and down to Abingdon in the south.
His stewardship has reaped a handsome dividend.
Oxford West and Abingdon was one of the key marginals the Tories had to regain to stand any chance of toppling Labour.
William Hague visited Abingdon on Tuesday, drumming up support, but to no avail.
Ed Matts said: "I have made many friends during the campaign and we raised many important issues which the public wanted discussed.
"We fought a tremendously good campaign and I hope in the future that the Conservatives will be back in Oxford West and Abingdon."
Check out the full Oxford West and Abingdon results
Check out the full national results
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