NBC Philadelphia / Justin Pizzi
"A win for the people, over the establishment, over the status quo, even over Washington D.C.," Sestak declared as he delivered his victory speech Tuesday night.
Beaming ear-to-ear, Sestak thanked a packed room of supporters at his election night headquarters inside the Valley Forge Military Academy in Wayne, Pa.
"Thank you Pennsylvania...this is what democracy is all about," he said. "I'll never forget that it was the people of Pennsylvania that made this happen."
Sestak, a two-time Congressman who spent 31 years in the Navy before running for U.S. House, will now face off against GOP candidate Pat Toomey in November.
"It should come as no surprise to anyone that the people want a change," Sestak said adding that there are too many "career politicians" in our nation's capital.
Pennsylvania Democrats have certainly made a huge change by throwing their support behind Sestak. His primary win leaves five-term Sen. Arlen Specter out of a job.
Specter switched to the Democratic side of the aisle last year after casting the critical vote in the Recovery Act. But, many believed he switched parties because he would have lost a Republican primary against Pat Toomey.
But even before Tuesday's vote, it seemed Specter was done anyway. In the days leading up to Tuesday's vote, Specters biggest supporters -- President Obama and Vice President Biden -- didn't come out to stump for the venerable pol.
Obama avoided Pa. altogether in recent days, staying away from the Keystone State even while he spoke in nearby Ohio.
Meanwhile, Biden kept a low profile as he dealt with his son's hospitalization and daughter's graduation from the University of Pennsylvania.
The White House said late Tuesday that the Vice President offered to help the Specter campaign, but that they didn't ask him to make a personal appearance. They went on to say Biden did do radio interviews.
With 99-percent of precincts reporting, Sestak received 562, 037 votes, or 54 percent; Specter received 479, 934 votes, accounting for 46 percent. The race was marred by low voter turnout likely caused by rainy weather and voter apathy.
Specter amazingly only carried three of the commonwealth's 67 counties -- Philadelphia, Dauphin and Lackawanna. The latter two were only won by narrow margins, but in his hometown, Specter was able to get 64-percent of the vote.
Sestak was the clear winner in the Philly suburbs -- parts of which he represents in Congress.
After the AP declared Sestak the winner just after 10 p.m., Specter appeared to address his supporters while they chanted, "Arlen, Arlen."
Specter said he called Sestak to congratulate him and tell him "I think it's vital to keep this seat in the Democratic Party and I will support him."
After nearly five decades in politics this loss likely spells the end for the 80-year-old Specter.
Fan, follow and download: Get the latest from NBCPhiladelphia.com anytime, anywhere. Follow us on Twitter, Facebook and NBC Philadelphia. Sign up for our breaking news newsletter. And, get breaking news delivered right to your mobile phone -- just text PHIBREAKING to 639710 to sign up. (Message and data rates may apply.)