The Olympic Stadium outfit fought back from a goal deficit with two second-half efforts to grab their eighth win of the season.
Douglas Santos’ 25th-minute opener gave the Hamburgers the lead but the Old Lady had to wait until the 56th minute to find a response through Valentino Lazaro who turned a Marvin Plattenhardt cross home.
Three minutes after the hour mark, Kalou was introduced for Maximilian Mittelstadt - his third substitute appearance this season - and the former Chelsea attacker wasted no time to repay Pál Dárdai's faith in him by netting the match-winning goal in 66th minute.
The Cote d’Ivoire international has now registered 10 goals in 24 league appearances this campaign.
The result moved Hertha Berlin to the 11th spot in the Bundesliga log with 35 points from 27 games - five points adrift of an Europa League place.