The four-time major winner, who has played in every Presidents Cup since its inception in 1994 and is undefeated in his last 11 matches, including one Saturday morning, will get the afternoon off in Melbourne.
Mickelson is getting a break to be ready for Sunday's singles, despite going 3-0 in the competition and holing a long birdie putt to close out his match.
"He's got an unbelievable record, but he's no longer 38, 40, 42, years old,'' Couples said. "And he wants to be ready to go in singles. I mean, that's not really an answer but that's the best I can tell you.''
Actually, Lefty is 41. Couples, known for his doublespeak and convoluted interviews, basically said that Mickelson had volunteered to sit out.
The format calls for five morning and five afternoon sessions during the third day of the Presidents Cup, meaning two players from each team do not play.
Couples is also giving 44-year-old David Toms a rest in the afternoon fourball session, better known as best ball.
"We talked about it, and I wanted to take the afternoon off if it was possible,'' Mickelson said after completing a 2 and 1 victory with partner Jim Furyk over Jason Day and Aaron Baddeley. "Fred thought everybody was playing well and we had some good pairings to send out. It gives me a chance to get ready for my singles match. And I like being out there and supporting the guys.''
The U.S. team took an impressive 11-6 lead in the competition during foursomes (alternate shot) on Saturday at Royal Melbourne, where the Americans won four of five matches.
Woods had been the only U.S. player without at least a half point through the first two days, and he made a 15-foot birdie putt on the 16th hole to close out the match. It was the longest putt he made all day.
"It was a day of patience,'' said Woods, who will play with Johnson again Saturday afternoon in fourball. "The weather is kind of iffy. The greens are another different speed, third different one. They got us some tricky pins out there. I felt Dustin and I were hitting the ball well. We kept the heat on, and eventually one would fall. Unfortunately it didn't happen until the last hole.''
Mickelson and Furyk played for the third straight match and rallied from a 2-down deficit through five holes.
Lefty is 12-1-5 at the Presidents Cup going back to the 2005 competition and has just one defeat in his last 18 matches. He had played in 32 straight Presidents Cup matches and is now 18-13-10 overall.
"He's played three straight matches and we want him really fresh for the singles,'' Couples said. "And he asked to sit, if need be, the same as David Toms.''
While the move appears curious, it's hard to argue with the American success to this point. Couples has seen Bubba Watson and Webb Simpson win three straight matches from the leadoff position. And the Mickelson-Furyk pairing also got him three points.
Although the U.S. has a big lead, the afternoon session began with half the matches in the competition remaining -- five fourballs and 12 singles on Sunday. A team needs 17.5 points to win the Presidents Cup.
Bob Harig covers golf for ESPN.com. He can be reached at BobHarig@gmail.com.