Katie McGinty

PHILADELPHIA —- Katie McGinty won the Democratic nomination for U.S. Senate Tuesday night, beating Joe Sestak with a late surge fueled by millions of dollars and high-profile party support from Washington.

McGinty, of Wayne, was declared the winner just before 10:30 p.m. according to unofficial results from The Associated Press.

The early returns showed a substantial margin far larger than many pollsters predicted.

Sestak, a retired admiral and former congressman from Delaware County, was in second with Braddock Mayor John Fetterman running a surprisingly close third, powered by a first-place showing in his home county, Allegheny.

McGinty's win was a victory for the Democratic establishment, whose endorsements and spending elevated a candidate with deep party roots but who had never won an election and lagged in polls until the final stretch.

The results set up a matchup with the incumbent Republican, Sen. Pat Toomey, in a race with national implications — both parties see it as one of a handful that will decide control of the Senate.

For Sestak, the night seemed to bring an unorthodox political career to a halt, dashing the hopes of a man who nearly topped Toomey in 2010 — but who forever clashed with party leaders. Top Democrats in Washington and Harrisburg saw McGinty, Pennsylvania Gov. Tom Wolf's former chief-of-staff, as the better option.

Party strategists hope her push to become Pennsylvania's first woman senator will dovetail with a likely presidential nomination for Hillary Clinton.

McGinty, who touts her blue-collar Philadelphia roots, argued that she would present the most stark contrast with Toomey.

Her campaign underwhelmed at first — one poll had her down 10 points one month ago — but was lifted by $4.5 million in spending from the Democrats' Senate political arm and their allies; two campaign visits by Vice President Joe Biden; and a string of endorsements from major labor unions; Sen. Bob Casey, D-Pa., and even President Barack Obama — whose image and voice graced McGinty's television spots.

Sestak, after narrowly losing to Toomey in 2010, had worked nearly non-stop for a rematch - including walking 422 miles across the state early last year. But party leaders feared that his unpredictable methods could cost them a key race. And many found him obstinate.

Sestak, touting his independence, said his support came from grass-roots Democrats, not party powers — who he accused of cutting off his fundraising network.