The Texas senator scooped his own planned announcement Monday.
The former news anchor unseated incumbent Ted O'Brien.
They GOP now needs a net gain of four seats to claim the Senate for the first time since the administration of George W. Bush.
Amid the focus on Senate and gubernatorial races, Republicans notch a less-noticed but still important victory.
Republicans pick up Senate seat in West Virginia as Shelley Moore Capito is projected to win; Mitch McConnell survives tough challenge in Kentucky.