The Brazilian found the net, for the seventh time this season, in the 62nd minute following good work from Oscar Wendt.
Monchengladbach remain fourth, three points behind Borussia Dortmund, and have now won five league matches in succession, while Freiburg are third from bottom.
In the only other Bundesliga game on Sunday, Hannover 96 ended a seven-game winless run with a 2-0 home triumph over Eintracht Frankfurt.
Mame Biram Diouf's 25th-minute strike set Hannover on their way, and Frankfurt's task was made tougher when Martin Lanig was sent off for a second bookable offence 12 minutes after the interval.
Szabolcs Huszti took advantage by claiming his seventh goal of the season midway through the second half.
Frankfurt have just 11 points from 14 matches, the same tally as Freiburg.