Winger Valbuena took advantage of fine work by midfielder Abou Diaby to score the winner seven minutes from time for the former world and European champions, playing in a 4-3-3 formation instead of the usual 4-2-3-1.
Midfielder Carlos Hernandez surprised France keeper Steve Mandanda with a low angled shot from the edge of the box to put Costa Rica ahead on 11 minutes.
During warm-up, the players wore tee-shirts saying "Pour Lass" (For Lass) in a message to midfielder Lassana Diarra, who was ruled out of the World Cup by illness on Saturday.
Coach Raymond Domenech, who has faced heavy criticism since his side's Euro 2008 flop, left captain Thierry Henry on the bench, bringing on the Barcelona forward for the second half.
France, who needed Henry's infamous handball to qualify for the World Cup through a play-off at the expense of Ireland, looked in control for most of the game but need more to suggest they can make an impact in the June 11-July 11 finals.
