Rep. James Lankford (R-Okla.) won the Oklahoma Senate primary outright on Tuesday, making him the odds-on favorite to replace retiring Sen. Tom CoburnTom Coburn'Path of least resistance' problematic for Congress Freedom Caucus saved Paul Ryan's job: GOP has promises to keep Don't be fooled: Carper and Norton don't fight for DC MORE (R-Okla.) in the fall.

The Associated Press called the race for Lankford, who led former Oklahoma House Speaker T.W. Shannon (R) 55 percent to 36 percent with 58 percent of precincts reporting.

Lankford topped the critical 50 percent mark in the seven-way primary, avoiding an August runoff, where Shannon could have marshaled conservatives in an election likely to have lower turnout. 

A second-term congressman and junior member of House leadership, Lankford benefitted from Mississippi's surprise Senate runoff, which drew money and attention from national conservatives that could have otherwise been targeted at him. 

Shannon had been closing quickly on Lankford's early lead, buoyed by national Tea Party support, endorsements from Sen. Ted CruzTed CruzFEC faults Cruz on Goldman Sachs loans in rare unanimous vote CBO score underlines GOP tensions on ObamaCare repeal Republicans go to battle over pre-existing conditions MORE (R-Texas) and Alaska Gov. Sarah Palin (R) and hundreds of thousands of dollars in spending from the Senate Conservatives Fund.

Shannon, who is also of Native American heritage, would have been the Senate's second African-American Republican in the current session.

But instead, Mississippi pushed the race out of the national spotlight, and the cash-strapped Shannon struggled to maintain his momentum without more outside money. Lankford also got a boost from Coburn, who stopped short of endorsing him but attacked the outside groups running ads against him and complimented the congressman’s integrity in remarks Lankford used heavily in his final ad push.

Former Oklahoma state Sen. Steve Russell (R) and state Corporation Commissioner Patrice Douglas (R) advanced to a runoff for Lankford's House seat.

Updated at 10:20 p.m.