Showers pelted down late in the day and were forecast to continue into Saturday, but the rain arrived after Couples had completed a 5-under 66 at the Riviera Country Club for a 36-hole total of 8-under 134.
At age 51, Couples makes only an occasional appearance on the regular circuit. He won four times last year in his rookie season on the Champions Tour.
John Senden and J.B. Holmes both completed two rounds at 6-under 136 and Spencer Levin was also 6-under with three holes to play when darkness forced a stoppage of play.
Phil Mickelson was in a tie for 26th place at 141.
Couples last won on the regular tour at the 2003 Houston Open.
"I opened up with probably a 100-foot eagle putt that I made (at the par-5 first hole)," Couples said, "and then it just kept going. It was a nice day."
Couples will captain the American Presidents Cup team later this year, but he said he would not think about becoming a playing captain even if he won this week.
"I'm a Champions Tour player that plays a couple times on the PGA Tour, but no way," Couples said. "If I could win by 10, I would still say no way. But my goal is to play well tomorrow and Sunday and see what I can do."