Monte Carlo - Japan's Kei Nishikori lost his opening match of the clay season on Wednesday, with Asia's top player crashing to a 7-5, 6-4 defeat to Pierre-Hugues Herbert at the Monte Carlo Masters.
Fifth seed Nishikori reached the final here last year but will lose a chunk of ranking points after he hit 25 unforced errors and just 14 winners in succumbing to Frenchman Herbert.
Nishikori will now move on to Barcelona next week, where he owns two titles as he works on his clay form as the run-up to Roland Garros intensifies.
Herbert, who overcame Fernando Verdasco in the first round, struck 31 winners in his upset to avenge a three-set loss to Nishikori in Rotterdam earlier this season.
"I'm very happy to finally beat Kei," the 49th-ranked Herbert said.
"I was very confident with my defence.
"I came to the match with good feelings after the first round."
Nishikori lost the Monte Carlo final a year ago to 11-time champion Rafael Nadal.
Latest results from the fourth day of the ATP Monte Carlo Masters on Wednesday (x denotes seeding):
Daniil Medvedev (RUS x10) bt Radu Albot (MDA) 6-1, 6-2
Stefanos Tsitsipas (GRE x6) bt Mikhail Kukushkin (KAZ) 6-3, 7-5
Cameron Norrie (GBR) bt Marton Fucsovics (HUN) 7-6 (7/3), 6-3
Pierre-Hugues Herbert (FRA) bt Kei Nishikori (JPN x5) 7-5, 6-4
Fabio Fognini (ITA x13) bt Gilles Simon (FRA) walkover
Alexander Zverev (GER x3) bt Felix Auger-Aliassime (CAN) 6-1, 6-4