Calcavecchia, the co-leader after the first and second rounds at Walton Heath, was in cruise control at 10-under with six holes remaining before imploding when his accuracy off the tee deserted him.
A disastrous triple-bogey 7 at No. 13 -- after driving into the heather beside the fairway -- was followed by another dropped shot on No. 16.
The 1989 British Open champion salvaged something from his round with a neat birdie at the final hole.
Calcavecchia, bidding to become the fourth player to capture the British Open double, shot even-par 72 to put him at 7-under 209.
Frost shot a bogey-free 66, tied for lowest round of the week, while Cochran's 67 included a double-bogey 6 on No. 14.
Augusta native Larry Mize had 74 and is tied for 29th place, eight shots off the lead.
EUROPEAN TOUR: In Stockholm, Alexander Noren of Sweden shot a course-record 9-under-par 63 Saturday to extend his lead to 11 shots after the third round of the Nordea Masters.
Noren, who held a three-shot overnight lead, made seven birdies and an eagle in a flawless round on the Bro Hof Slott course and is now at 20-under 196.
He equaled the second largest third-round lead ever on the European Tour, behind Retief Goosen's 13-shot edge at the 2002 Johnnie Walker Classic.
Bubba Watson shot 69 to sit in second place, one stroke ahead of Christian Nilsson of Sweden and Jaco Van Zyl of South Africa.
LPGA TOUR: In Evian-Les-Bains, former champion Ai Miyazato of Japan took a two-shot lead at the Evian Masters, shooting 5-under-par 67 in the third round to move to 13 under overall.
Miyazato, who won her first LPGA title at the Evian Masters two years ago, made five birdies. She heads into today's final round ahead of a group of four players, including Kraft Nabisco winner Stacy Lewis. Overnight leader Miki Saiki of Japan, Ran Hong of South Korea and Angela Stanford are also at 11-under.
NATIONWIDE TOUR: In Columbus, Ohio, amateurs continue to hold down the top two spots in the Children's Hospital Invitational.
Former Louisiana State University golfer John Peterson (68 on Saturday) leads former Georgia golfer Harris English (68) by one shot for the second consecutive day.
Peterson, who won the NCAA Division I individual title in June, is at 14-under 199.
James Sacheck had 63 and is two shots back at 201.
Aiken native Matt Hendrix had 68 and is at 204 while North Augusta's Scott Brown had 70 for 210 and Swainsboro's Will Claxton had 72 for 214.