(CNN) -- Sen. Mitch McConnell trounced his tea party-backed opponent in Kentucky's Republican primary, leading a quartet of establishment GOP candidates to victories around the country Tuesday.
After an expensive and bitter campaign, the Senate minority leader led defeated challenger Matt Bevin 60%-36%, with 97% of precincts reporting, according to numbers compiled by The Associated Press.
In addition to Kentucky, more moderate candidates won in Republican Senate primaries in Georgia and Oregon and in a House showdown in Idaho.
And the results in Kentucky, Georgia and Oregon could improve the GOP's chances of taking back control of the Senate come November's midterm elections.
Democrats hold a 55-45 voting majority in the Senate. They're defending 21 of the 36 seats in play, half of them in Republican-leaning states or states where the two parties have similar levels of support.
The only states where the Democrats hope to play offense are Kentucky and Georgia.
If the GOP flips six Democratic held seats, they will win control of the Senate and McConnell will get a promotion from minority leader to majority leader.
"We can take the reins of power away from Harry Reid and make this President accountable," McConnell said in his victory speech. "Make me the majority leader, and Kentucky will lead America."
Here are rundowns in the other state races:
Georgia: Republican businessman David Perdue will face Rep. Jack Kingston in a runoff in July. Perdue got 30% of the vote; Kingston received 27%, according to numbers complied by The Associated Press. Perdue and Kingston beat out a trio of more conservative candidates in the GOP primary.
Among Democrats, Michelle Nunn easily won in her bid to follow in the footsteps of her father, longtime Sen. Sam Nunn.
Oregon: Sen. Jeff Merkley easily won the Democratic primary, and pediatric neurosurgeon Monica Wehby is the projected winner of the GOP Senate primary, topping a more conservative rival.
Idaho: Rep. Mike Simpson won the GOP primary in the state's 2nd Congressional District, defeating tea party candidate Bryan Smith.
Ugly and expensive race
Bevin, a businessman from Louisville, announced last summer he would challenge McConnell. He quickly gained the support of tea party activists and some influential Washington-based anti-establishment groups.
The race between the two men quickly turned ugly, and expensive, as both campaigns and outside groups spent big bucks.
The Senate Conservatives Fund dished out $1 million to support Bevin. But the group recently fell quiet with McConnell's formidable lead in public opinion polls.
McConnell had a large campaign war chest, as well as backing from two Kentucky-based super PACs, and such powerful national groups as the U.S. Chamber of Commerce and the National Rifle Association.
Calls for unity
Soon after the race in Kentucky was called for McConnell, two of the groups backing Bevin -- the Senate Conservatives Fund and the Madison Project -- closed ranks behind the Senate minority leader.
"Now it's time for Republicans to unite for victory in November," said a statement from the Senate Conservatives Fund.
McConnell now faces a much tougher test against Kentucky Secretary of State Alison Lundergan Grimes.
Grimes, considered a rising Democratic star, faced no real opposition in her primary and already has had big names -- such as former President Bill Clinton -- team up with her on the campaign trail.
Speaking to supporters who held up signs that read "Obama needs Alison Grimes" and "Kentucky needs Mitch McConnell," McConnell previewed his primary election theme: tying his opponent to President Obama, who lost Kentucky big in 2012 and is highly unpopular there now.
"My opponent is in this race because Barack Obama and Harry Reid want her to be in this race," said McConnell, adding that "a vote for my opponent is a vote for Obamacare and the President who sold it to us on a mountain of lies."
The pro-McConnell outside group Kentuckians for Strong Leadership said they would spend nearly $600,000 starting Wednesday to run a television commercial that ties Grimes to Obama.
Grimes, who spoke at her victory celebration just minutes after McConnell's speech ended, fired back.
"I'm here to tell you tonight, my fellow Kentuckians, I am not an empty dress, I am not a rubber stamp and I am not a cheerleader. I am a strong Kentucky woman who is an independent thinker who, when I'm Kentucky's next senator, the decisions I make will be what's best for the people of the Commonwealth of Kentucky, not partisan interests," Grimes declared.
She's expected to use McConnell's GOP leader status and his frequent moves to block legislation to make him the symbol of gridlock in Washington.
The most recent polling indicates the two candidates are all tied up.
When all's said and done, the race could become the most expensive Senate campaign in history, breaking the $82 million record set in the 2012 Senate battle in Massachusetts.
CNN's Steve Brusk, Dana Davidsen and Holly Yan contributed to this report.