The other candidates in the race draw a combined 7 percent of the vote, and 18 percent are undecided.
That’s a slight tightening of the race since Lankford’s last internal poll, conducted in mid-May, which showed him up 10 points over Shannon. And it's another out this week that indicates the race is headed towards a runoff.
A new survey out on Wednesday from a group supporting Shannon showed a tighter race, with Shannon lagging Lankford by 2 points, with 37 percent support to Lankford's 39 percent support. But that's a considerable decline in support for Shannon from the group's last poll, conducted in April, which showed him up 10 over Lankford.
With under two weeks left until the primary, however, the race could continue to shift.
Outside groups are still launching new ads, with the Senate Conservatives Fund airing one attacking Lankford this week. And Sen. Tom Coburn (R-Okla.) on Thursday weighed in on the race to replace him, praising Lankford and slamming those negative attacks.
The Lankford survey was conducted among 500 registered likely GOP primary voters via live cellphone and landline interviews, and has a margin of error of 4.5 percentage points.