Castro put the perfect finishing touch on this most wild day at Congressional when he hit his approach into the water left of the 18th green, and then chipped in for par from 80 feet to salvage an even-par 71 and keep a share of the lead.
Haas made nine birdies and had to settle for a 68, courtesy of two wedge shots that cost him four shots, including his triple bogey on the beastly 11th hole. Romero had a three-shot lead at one point, and then it was gone. He went from the water to a bunker on the 11th for double bogey and followed that with a bogey on the next hole. He made six pars the rest of the way for a 70.
Driscoll, meanwhile, motored along without too much excitement. He had a 68, the only player in the field to break 70 in all three rounds. Coming off a bogey on the 15th, Driscoll though he might be headed for another with a poor tee shot. But he knocked a 4-iron out of the rough, barely got onto the green and rolled in a 25-foot birdie.
They were at 7-under 206, and more fun awaits on Sunday.
"I think over four days here, every player is going to hit kind of a rough patch," Castro said.
Ten players were separated by four shots going into the final round, a group that includes 19-year-old Jordan Spieth. He had a two-shot lead after opening with two straight birdies, and then went through a stretch of missing five putts inside 8 feet oover four holes. One of them was a three-putt from 5 feet for double bogey on No. 8. Spieth had a 74, though he's still in the game, just three shots behind.
"A wild day," Castro said.
Jason Kokrak had a 70 and was one shot out of the lead, while Charlie Wi had a 29 on the front nine and shot 65 to finish two shots behind, along with Tom Gillis (66). Spieth was in the group at 209 with Brandt Snedeker, who had a 69.
If Saturday was any indication, expect anything in the final round, especially since seven of those 10 players have never won on the U.S. PGA Tour.
Leading scores on Saturday after the third round of the $6.5 million US PGA National at par-71 Congressional Country Club (USA unless noted):
206 - Bill Haas 70-68-68, James Driscoll 69-69-68, Roberto Castro 66-69-71, Andres Romero (ARG) 70-66-70
207 - Jason Kokrak 71-66-70
208 - Tom Gillis 70-72-66, Charlie Wi (KOR) 72-71-65
209 - Brendon Todd 74-67-68, Brandt Snedeker 69-71-69, Jordan Spieth 69-66-74
210 - Morgan Hoffman 73-68-69, Brendan Steele 73-71-66, Stewart Cink 70-69-71, Nicolas Colsaerts (BEL) 69-68-73
211 - Fabian Gomez (ARG) 69-73-69, Chad Campbell 72-70-69, Ken Duke 71-70-70, Graham DeLaet (CAN) 68-72-71, Gary Woodland 70-69-72
212 - Rickie Fowler 71-71-70, Camilo Villegas (COL) 71-70-71, Angel Cabrera (ARG) 70-70-72, Martin Flores 73-71-68, David Lingmerth (SWE) 74-65-73, Shawn Stefani 70-74-68, Lee Dong-Hwan (KOR) 71-66-75
213 - John Huh 71-71-71, Nicholas Thompson 73-69-71, Richard Lee 74-68-71, Brian Davis (ENG) 70-72-71, Adam Scott (AUS) 73-71-69, David Mathis 71-70-72, Cameron Tringale 71-67-75