All four golfers are 13-under-par 203, one-stroke better than Nick O'Hern (66) and Carl Petterson (67).
Leonard, the second-round leader, squandered his advantage with two bogeys on the back nine, finishing with a 1-under 71.
"In general, (I) just didn't putt as well today as I have the previous two days," Leonard said.
Rose (69) made four birdies in a six-hole span on the back nine, but a bogey at the 17th kept him from taking the outright lead.
Gronberg shot six-under 66, including six birdies -- five on the back nine -- and no bogeys.
McNeill shot 3-under 69 and seeks his second win this season in Sunday's fourth round.