Alexander Zverev crashed out of the Indian Wells Masters, while rain wreaked havoc for world number one Novak Djokovic.
German third seed Zverev was stunned by countryman Jan-Lennard Struff in straight sets in the third round on Monday.
Milos Raonic, Dominic Thiem and Ivo Karlovic also progressed to the last 16 at the ATP 1000 tournament.
Djokovic, however, was halted by rain with the top seed leading Philipp Kohlschreiber 1-0 in the opening set before the match was suspended in the California desert.
Zverev shocked by compatriot
Struff produced the upset of the tournament thanks to his stunning 6-3 6-1 victory against Zverev.
World number 55 Struff blitzed Zverev in 70 minutes, losing just three of his first-serve points while saving all four break points he faced.
"It's amazing," Struff said. "I played a good match. He was missing some shots today, but at the end of the day I'm very happy with that [performance]."
Raonic rallies past Giron
Canadian 13th seed Raonic awaits Struff after his come-from-behind 4-6 6-4 6-4 victory against Marcos Giron.
Raonic lost the first set and was down a break at 4-1 in the third before rallying into the round of 16 for the sixth successive year.
"He came up with the goods and definitely pushed me sort of to the brink there where I was getting a little bit frustrated," Raonic said. "I just kept trying to plug away."
Thiem dominates Simon
It was a routine match for seventh seed Thiem, who defeated Gilles Simon 6-3 6-1.
The win continued Thiem's dominance against Simon, with the Austrian having now won eight consecutive matches against the Frenchman.
Croatian veteran Karlovic is next up after the 40-year-old beat qualifier Prajnesh Gunneswaran 6-3 7-6 (7-3).
Karlovic – who became the oldest match winner at a Masters 1000 event since the level was created in 1990 after his first-round victory – will be looking to reach his first Masters quarter-final since 2011.
Monfils sets up potential Djokovic clash
Entertaining Frenchman Gael Monfils could be set for a showdown with Djokovic following his 6-0 6-3 win over Albert Ramos-Vinolas.
Monfils – the 18th seed – will face the winner of the match between Djokovic and Kohlschreiber for a place in the quarter-final.