Sacrificial lambs that ended up winning the election

[Miles]

Chip Cravaack. The last time Oberstar was held under 60% was the year I was born (1992).

[Miles]

Surely Kay Hagan, wasn't she an unknown State Senator before 2008?

Hagan was definitely an underdog, but I wouldn't really say she was a "sacrificial lamb." IIRC, there were signs early on that Dole could be vulnerable.

You could also say that about Joni Ernst. A previously low-profile state senator who ran in a race where she was initially the underdog. Both won by about the same margin, too. 

[Miles]

Maybe not a sacrificial lamb, but I'm sure Steve Stockman beating Jack Brooks in 1994 is worth mentioning. By the early 90s, Brooks was winning by smaller margins that he was used to, but OTOH, 1994 was Stockman's third run at the district, so he was probably approaching perennial candidate status.