Read & Watch Hot Shots: Herbert Upsets Nishikori For Third Top 10 Win
Frenchman, who is focusing more on singles in 2019, faces Coric on Thursday
The Open Sud de France runner-up found his best level in the big moments, saving all 10 break points he faced to advance after one hour and 42 minutes. Herbert's first victory over Nishikori in three FedEx ATP Head2Head encounters is also the Frenchman's first Top 10 victory on clay. Herbert owns a 3-11 overall record against Top 10 opposition.
"This was a very nice victory. Probably one of the nicest on clay and probably one of the nicest of my career, so I am really excited about it," said Herbert.
"I'm very happy for this victory, but we shouldn't exaggerate. I had 10 break points that I had to save and I'm happy that I managed to play good in the difficult points. It was tricky, because it wouldn't have taken much for him to take the advantage."
Herbert will meet ninth seed Borna Coric for a place in the quarter-finals. The World No. 49, who is aiming to reach his third quarter-final this year, lost his only previous FedEx ATP Head2Head clash against Coric at the 2017 Mutua Madrid Open. Alongside his run to the Open Sud de France championship match (l. to Tsonga), Herbert opened his season with a run to the last eight at the Qatar ExxonMobil Open (l. to Berdych).
"[Coric] has spent lots of time on clay, so it's going to be a big challenge tomorrow for me," said Herbert. "Again, I'm not going to be the favourite, of course, but on my side, I also won two difficult matches, so why not?"
On Court 2, Cameron Norrie captured his 10th tour-level victory of the season (10-8). The 23-year-old, who reached the ASB Classic final in January (l. to Sandgren), defeated Marton Fucsovics 7-6(3), 6-3.