The Eagles held their visitors to a goalless draw in the opening 45 minutes of Tuesday's game but their resistance was finally broken when Timo Werner opened the scoring nine minutes after the hour-mark.
In the 78th minute, Werner doubled RB Leipzig's lead with his second goal of the night but Haris Seferovic's 84th-minute effort reduced the deficit for the hosts.
Taarabt was in action for Benfica for the duration of the match but his contribution was not enough to help the Eagles start their campaign on a flying note.
At the end of the game, the Morocco international rued the defeat and has called on his teammates to focus on their upcoming Primeira Liga matches before they battle Zenit St Petersburg in their next Group G outing on October 2.
"It wasn't the result we wanted, but let's keep working and focused on the next game," Taarabt wrote on Instagram.
Tuesday's loss at Estadio da Luz left Benfica at the bottom of Group G after Lyon and Zenit settled for a 1-1 draw at the Groupama Stadium.