Shadow Scottish Secretary Peter Duncan has been defeated by Labour's Russell Brown in the hotly contested Dumfries and Galloway seat.
Peter Duncan was the sole Scottish Tory MP for four years
The only sitting Tory MP and Commons counterpart Mr Brown were thrust together in this contest following boundary changes.
Mr Duncan polled 18,022 votes but Mr Brown was almost 3,000 votes ahead on 20,924 - a notional Labour hold.
It was a major setback in the Tories' continued revival bid in Scotland.
The Tories were well aware that the new seat had a theoretical Labour majority of 141.
Mr Duncan took the seat of Galloway and Upper Nithsdale from the Scottish National Party in 2001, with the lowest Conservative majority in the Commons.
Mr Brown has been MP for Dumfries since 1997. He stepped down as a parliamentary aide to the leader of the House of Lords in 2003 in protest at the Iraq war.
Mr Duncan, who was elected Scottish Tory chairman last year, had been at the forefront of their campaign and was a high-profile loss, compensated by party colleague David Mundell's success in Dumfriesshire, Clydesdale and Tweeddale.
Contemplating his defeat, Mr Duncan consoled himself with the thought that a colleague had kept the Scottish Tory flag flying at Westminster.
He told BBC Scotland: "Clearly it's a personal disappointment but I think we have shown that in the south of Scotland we can still win constituencies.
"We have a longer term ambition to build on that and make the solution to Scotland's problems - building problems under Labour - the Scottish Conservative solution."
The Tories' big rivals in the old seat had been the SNP but this time round candidate Douglas Henderson polled 6,182, 12.1% of the vote, with Keith Legg of the Lib Dems on 4,259 (8.3%).
Mr Duncan said: "There were clearly some very big vote shifts going on tonight.
"I think when you get a new constituency boundary people are looking around for how the first vote comes out to establish where their voting priorities will lie but our task is to build upon the issues that matter and seek to build upon that for the future."