The Philadelphia district had been served by longtime state Sen. Vincent Fumo, who's facing federal corruption charges. He's leaving at the end of this term.
None of the other 25 senators whose terms expire this year faced any opposition from within their own parties. The other half go before voters in 2010.
A Democratic state representative from Philadelphia lost a primary challenge on Tuesday, but at least 24 other incumbent Pennsylvania lawmakers won nominating contests.
Rep. Harold James, a former police officer and 20-year veteran of the General Assembly, lost to community organizer Kenyatta Johnson.
Two years ago, 24 incumbents lost and 31 retired in the face of voter outrage over the short-lived pay raise law.
Tuesday's results are already shaping fall campaign strategies. Democrats are looking to pick up seats in Philadelphia and its suburbs to strengthen their now-tenuous control in the House, while Republicans hope for gains in the southwest and in rural areas.
This year's elections are not expected to change the balance of power in the Senate, where the GOP holds a 29-21 advantage.
But control of the House could be in play. It is split 102-101 in favor of the Democrats, with Speaker Dennis O'Brien, R-Philadelphia, usually voting with the Democrats. The Democrats elevated O'Brien to speaker in 2007.
The stakes are high for Democratic Gov. Ed Rendell, who is heading into his final years in office hoping for action on his health care, energy and economic initiatives.
General election campaign issues may include the tolling of Interstate 80, last summer's budget stalemate, the ongoing investigation into the use of legislative staff for electioneering, charges against the owner of a Poconos casino and an ambitious Democratic agenda that Republicans have effectively stymied.
Ninety-four representatives - half Democrats, half Republicans - and five state senators have no opposition this year.
