The former Germany international was appointed as South Korea's new coach last week, replacing Hong Myung-bo, and looked on from the stands at the Goyang Stadium.
It could not inspire the hosts, though, as Uruguay – playing their second game since a last 16 exit at the World Cup – proved too good.
The visitors, missing the suspended Luis Suarez, dominated the first half but failed to score and when they did have the ball in the back of the net in the 62nd minute, Abel Hernandez's effort was disallowed.
South Korea then had a golden chance to take the lead when Ki Sung-yueng's lofted pass found Son Heung-min on his own.
But with the goalkeeper to beat, Son could only shoot straight at Martin Silva.
And Gimenez made the hosts pay with 20 minutes left when he rose above Kim Joo-young to head in Giorgian de Arrascaeta's free-kick from near the by-line.
Gimenez's near-post header was almost cancelled out by Ki with five minutes to play, but the Swansea City man nodded his his effort onto the crossbar.
