Senate Democrats won all three of their targeted races, picking up seats vacated by retiring Republicans in Erie, suburban Pittsburgh and Harrisburg. In the House, Republicans gained one seat but five incumbents were locked in tight contests.
The Senate Democrats' campaign coordinator said the results will transform business in the Capitol, arguing his Republican counterparts will need the votes of moderate members in the Philadelphia suburbs.
"This changes the entire dynamic in Harrisburg," said Sen. Daylin Leach, D-Montgomery. "Keep in mind, we passed a lot of extreme legislation. Often three or four Republicans would break away—they still had the votes to pass it. Now they're going to need virtually every Republican on every vote."
Voters flipped at least one House district, electing Republican Thomas Sankey III to a Clearfield County seat opened by the retirement of veteran Democratic Rep. Bud George, who did not run again after serving 19 two-year terms.
The House has been in GOP hands, ending the current two-year session with a 111-92 margin. In the five uncalled races, three incumbent Republicans were trailing and two held narrow leads.
In all five races, at least 85 percent of the votes had been counted.
The Senate has been at 30-20, so the margin next year will narrow to 27-23.
Along with Republican Gov. Tom Corbett, the GOP majority has been struggling to adapt to sluggish state revenues in recent years. The closer margin could have implications for the governor's agenda on education, transportation, pensions and other issues.
The House will have two immediate vacancies, as Rep. Eugene DePasquale, D-York, defeated a fellow state representative for a four-year term as auditor general, and Rep. Matt Smith, D-Allegheny, was elected to the Senate. Smith was unopposed in his House race and DePasquale won another House term.
The Senate Democratic advances were in districts held most recently by Republicans Jeff Piccola in Dauphin County, John Pippy in Allegheny County and Jane Earll in Erie County.
Veteran lawmakers who lost in spring primaries include 14-term Rep. Babette Josephs, D-Philadelphia, and 17-term Rep. Rick Geist, R-Blair.