Two goals from Jimmy Briand proved to be in vain as Claudio Ranieri's high-flying Monaco side secured all three points at Stade de Gerland.
Saint-Etienne's defeat to Paris Saint-Germain means Lyon remain just three points behind Christophe Galtier's fourth-placed side in the race for a UEFA Europa League place with nine games remaining.
And Garde was proud of his players' efforts on Sunday, just three days after they hammered Viktoria Plzen 4-1 in the first leg of their UEFA Europa League last 16 tie.
"We believed until the end. Remember, we played against a very good Monaco team with world-class players who can make a difference. Monaco are second in the table on merit," he said.
"We spent a lot of energy in the Europa League on Thursday but we were able to put (Monaco) under pressure in the second half. This was our 48th game of the season.
"There is a lot of physical fatigue but the group is remarkable and we can be optimistic of big things happening by the end of the season."
