By the way, Humbert doesn't qualify with only 8 such matches, but if I had lowered the minimum to 8 matches, he'd lead the entire NextGen with his 5-3 record (62.5%).
He is still young and hasn't played many top10, so it's not really surprising.
I'm pretty sure he beat Nishikori twice in a row in 2019, when Nishikori was still top-10.
This year beat Rublev and Tsitsipas in Miami, and Medvedev and Federer in Wimbledon.
That's already 6 top-10 and like I said, he hasn't played many.