Pennsylvania's longest-serving U.S. congressman, Tim Holden, was defeated in a Democratic primary election.
Matthew Cartwright, a lawyer who criticized Holden for his opposition to President Barack Obama's healthcare law, defeated the 10-term Democrat in Tuesday's election, according to the Pennsylvania Department of State's preliminary findings.
The district in northeastern Pennsylvania was redrawn since Holden, a member of the Blue Dog Coalition of moderate Democrats, last ran for re-election to include more liberal urban areas.
It was not the only upset in the state's busy primary day.
In one closely watched race, Representative Mark Critz edged out fellow Democratic incumbent Jason Altmire in a contest to represent a newly combined congressional district near Pittsburgh.
Pennsylvania is due to lose one congressional seat as a result of the once-per-decade redistricting process, and the Republican-controlled state legislature combined the seats represented by the two Democrats, creating a new 12th District.
While Altmire was initially favored to win because his former constituents formed a majority of the new district, Critz won important union endorsements and the backing of former President Bill Clinton.
And in the five-way Republican race to take on Democratic Senator Robert Casey in November, political newcomer Tom Smith emerged victorious with nearly 40 percent of the vote, trailed by Sam Rohrer and Steve Welch, who each took about 20 percent of the vote.
Casey easily beat challenger Joseph Vodvarka, winning 80 percent in the Democratic primary.
(The story has been refiled to fix typo in the first paragraph.)