Republican Dave McCormick won the U.S. Senate election in Pennsylvania, Decision Desk HQ projected on Thursday, beating Democratic incumbent Bob Casey in an important win for Republicans hoping to capture a majority in the chamber.

One of Pennsylvania's two U.S. Senate seats is before voters Tuesday, with Sen. Bob Casey vying for a fourth term against challenger and businessman Dave McCormick. It is expected to be a close race and could ultimately play a role in the balance of power in the Senate.

Unofficial returns in the race between Senator Bob Casey and Dave McCormick have triggered a mandatory recount under state law.