Of the 50 hottest races for Republican-controlled congressional districts, Democrats flipped more than 30 seats. Votes in 10 House districts are still being tabulated and remain competitive for the minority party.

Notably, 15 of those 50 seats were left open after the Republican incumbent did not run for re-election.

Republicans’ giving up home field advantage in those districts seemed to have further buoyed Democratic efforts to take control of the House.

Democrats gained the most ground in Pennsylvania this election cycle — a state that helped President Donald Trump win the White House — where three of the contests were for open seats.

Oklahoma’s 5th Congressional District served up one of the biggest surprises among the House races, with Democrat Kendra Horn defeating Republican incumbent Steve Russell in a district controlled by the GOP for more than 40 years.

But certain Republicans were also able to hold ground despite strong Democratic challengers. At least eight hotly contested GOP seats remained in Republican hands as of Wednesday morning. Most notably, Rep. Andy Barr hung onto his Kentucky seat after facing a powerful test in former Marine fighter pilot Amy McGrath, whose campaign efforts earned national attention.

Get NBC's full 2018 midterms news and election results here.