World No 1 Novak Djokovic was dumped out by Daniil Medvedev while Rafael Nadal survived a struggle to reach the semifinals of the Monte Carlo Masters for the 14th time on Friday.
Djokovic, twice a champion in the principality, lost serve five times in a 6-3, 4-6, 6-2 defeat by Russia's 10th seed Medvedev.
Nadal, an 11-time winner of the event, rallied from 4-1 down in the opening set before finally overhauling Argentina's Guido Pella 7-6 (7/1), 6-3.
The Spaniard will face off in Saturday's semifinals against Italian Fabio Fognini, who came back to beat Croatia's ninth seed Borna Coric 1-6, 6-3, 6-2.
Nadal stands 11-3 in the series, having won their last six matches.
Novak Djokovic was dumped out of the tourney by Daniil Medvedev
For Djokovic, who won a record seventh Australian Open title in January, defeat marked another premature exit after he crashed out in the early rounds at Indian Wells and Miami last month.
The Serb, who has won the last three Grand Slam events and could conclude a personal sweep with another title at Roland Garros in June, feels that all he needs is more court time and some extra polish.
"The French Open is the ultimate goal on clay. It's expected in a way for me to peak right at that tournament, because that's what I'm aiming for," Djokovic said.
"This is only the first tournament on clay, and it's a long season. Let's see how it goes.
"Maybe I'm lacking the consistency with the top results in the last couple of years in the best tournaments.
"But I've been playing my best at Grand Slams and that's what I intend to do."
Djokovic was broken three times in the final set, clawing one back but exiting when Medvedev drove a backhand into the far corner on match point.
Nadal toiled away for two hours, 20 minutes to win for the 71st time in 75 matches at the tournament.