The Ivorian forward guided the Old Lady to hand Dieter Hecking's men their first league defeat at the Borussia Park
Salomon Kalou ended his 11-game goal drought after netting the opener in Hertha Berlin's 3-0 win over Borussia Monchengladbach on Saturday.
The former Chelsea star last scored a goal in October; a brace that earned Pal Dardai's side a 2-2 draw against Borussia Dortmund.
After a cagey affair between both sides in the opening minutes, Kalou broke the deadlock on the half-hour mark with his third league goal of the campaign.
The Cote d'Ivoire international maneuvered past Monchengladbach defenders before placing his shot beyond goalkeeper Yann Sommer's reach.
The effort was the 33-year-old's sixth in 10 outings against the Borussia outfit, making them his favourite goalscoring opponents alongside Hannover 96.
After the interval, Ondrej Duda and Davie Selke sealed maximum points for the visitors in the 56th and 76th minutes respectively to secure their second league win in 2019.
The defeat for Borussia Monchengladbach was their first on home ground since the start of the 2018-19 league campaign.
Hertha climbed to seventh spot in the Bundesliga standings with 31 points from 21 games and they return to action against Werder Bremen at the Olympic Stadium next Saturday.