David Toms, Hideki Matsuyama, Chad Campbell and Chris Stroud shared the third-round lead at 7-under 203 on Saturday at Colonial, where plenty of others also are in contention.
There were 13 players within two shots of the quartet in Fort Worth, Texas.
"It's kind of jammed in there," Campbell said.
The closest chasers include Adam Scott, the No. 1 player in the world, and Jimmy Walker, a three-time PGA Tour winner this season and No. 1 in the FedEx Cup standings.
Kevin Chappell, whose early 7-under 63 was the low round of the day at Colonial, moved from a tie for 60th to within a shot of the lead.
"I used up a lot of luck today. I had two chip-ins and made some long putts. Fifth-nine would have been nice, but kind of lost the feel of the putter on the back nine," Chappell said.
Matsuyama shot a 64. Toms, who got the last of his 13 tour wins at Colonial in 2011, had a 65. Local resident Campbell shot a 68, and Stroud had a 69.
Walker was 6 under after a 69, and Scott was another shot back after a 66.
Champions: Colin Montgomerie took the lead in the Senior PGA Championship, making a 30-foot birdie putt on 18 for a 3-under 68 at Benton Harbor, Michigan.
The Scotsman, trying to win his first senior major after failing to capture one of golf's four biggest events on the regular tours, had a 7-under 206 total at Harbor Shores.
Bernhard Langer was a shot back after a 70. Marco Dawson (64), Bart Bryant (70) and Kiyoshi Murota (70) shared third at 5 under. Second-round co-leader Tom Watson had a 72 to drop four shots behind.
LPGA: Anna Nordqvist moved into position for her third title of the year, shooting a 6-under 66 to take the lead in the Airbus Classic in Mobile, Alabama.
The Swede had a 16-under 200 at the Robert Trent Jones Golf Trail's Magnolia Grove complex.
Catriona Matthew was a shot back after a 70. She bogeyed three of the first five holes.
Stacy Lewis, who needs to finish solo third or higher to take the top spot in the world from Inbee Park, was third at 14 under after a 66. Park missed the cut Friday.
Michelle Wie (66), Jessica Korda (69) and Charley Hull (71) shared fourth at 13 under.
European: Thomas Bjorn birdied seven of his last eight holes to take a five-shot lead at the BMW PGA Championship in Virginia Water, England.
The Dane rallied from a double bogey on the first hole by making six straight birdies from the 11th and adding another one at 18 for a 5-under 67 and a 15-under 201 total at Wentworth.
Luke Donald was second after a 68. Shane Lowry (73) was third at 207, a shot ahead of Rory McIlroy (69).
Webcom: Former Cal star Max Homa struggled to a 3-over 74 and trailed leaders Byron Smith, Hunter Haas and Harold Varner III by five shots at the Rex Hospital Open in Raleigh, North Carolina. Homa, who won last week's tour stop, shared ninth at 6-under 207 at TPC Wakefield Plantation.