Appleby, who led the Masters after three rounds in 2007 but finished tied for seventh, said no matter who was chasing, he did not think it would ever pay to be too at ease in a major.
"They're not supposed to be comfortable," the 37-year-old said.
"That's sort of why there's only four of them a year, and they're
always on testing golf courses."
Appleby capped off his round with a 45-foot birdie putt at the 18th hole.
"Typical stuff when you are at 50 feet. You try to use your natural feel," Appleby said.
"Knocked it on to about 45 feet. Bingo."
Appleby, who won two of US tour victories in 2006 and also owns seven Australian tour titles, said experience had made him more able to deal with the pressure of contending in a major.
"I think as you get older you've got to find a way to be more comfortable," he said.
"I guess effectively by trying to gain control out here you've got to let go of control. That's sort of not a natural thing to do, that's why it's so difficult."
Appleby said his experience at the Masters last year, when he faded as Zach Johnson stared down Tiger Woods for the win, had been a learning experience.
"Hanging in there is what you've got to do," he said. "Morally that gives you a victory, maybe even if it doesn't turn out to be a victory."
Two spectators were arrested on Friday after becoming embroiled in a scuffle with Australian Adam Scott's caddie.
According to a San Diego police spokesman, the spectators heckled world number three Scott and his caddie Tony Navarro on the par-five ninth hole at Torrey Pines.
Navarro ducked under the ropes that keep fans off the course to confront the pair, a father and his son. After a brief physical exchange, Phil Mickelson's caddie Jim 'Bones' Mackay intervened to help Navarro.
The two spectators, who had earlier distracted Australian Stuart Appleby on the adjacent 18th tee, were eventually led away by San Diego police.
"They were being a little loud and a little rude," world number one Tiger Woods said of the two fans after carding a three-under-par 68.
Woods played the first two rounds at Torrey Pines in the company of Scott and fellow American Mickelson.
"Stuey is over there on 18 trying to tee off and Tony [Navarro] is trying to make sure that he [Appleby] doesn't have these guys yelling on his swing," Woods said.
"They didn't like that very much."