Thierry Henry’s young team are floundering in Ligue 1, sitting second-bottom and five points from safety, but managed to keep their coach’s hopes of a first trophy alive at the Stade Louis II.
“That’s exactly how we want to play,” said the former Arsenal and France striker. “Sometimes we heard the crowd were unhappy, but we got the ball back on the ground and we played.
“Finally we reacted after conceding a goal. Before we didn’t know how to do it. This time, we did.”
Monaco were the better side for the majority of an uneventful first half, with Moussa Sylla twice going close, but went into the break a goal down after Benjamin Bourigeaud swept Rennes ahead on the half-hour mark after a clever pass from Hatem Ben Arfa.
Henry was grateful to have Lopes back in the starting line-up for the first time since September 2 after a thigh injury, and the Portuguese forward tapped in Julien Serrano’s low cross to level in the 54th minute.
Kamil Glik and new signing Naldo both missed chances to win the tie for Monaco on penalties, but 20-year-old Badiashile slotted home the 22nd spot-kick to send them through after Rennes ‘keeper Tomas Koubek had blazed over.