Serbia's 61st-ranked Miomir Kecmanovic shocked sixth-seeded Matteo Berrettini 6-3, 6-7 (5/7), 6-4 on Wednesday to book a quarter-final clash with Taylor Fritz at the ATP Indian Wells Masters.
The 22-year-old Kecmanovic equalled the biggest win of his career as he reached the last eight of a Masters level event for the second time.
Berrettini, runner-up to Novak Djokovic at Wimbledon in 2021, is at a career-high sixth in the world after reaching the Australian Open semi-finals in January.
But he couldn't find the answer against an aggressive Kecmanovic, who pressured Berrettini's serve throughout.
Unable to convert two break points in the eighth game of the final set, Kecmanovic broke Berrettini to love in the final game, letting out a shout of triumph as the Italian sent a forehand wide on match point.
Kecmanovic will now be hoping to go further than his quarter-final run in the California desert in 2019.
Standing in his way will be 20th-seeded American Fritz, who shook off a slow start to beat Australian Alex de Minaur 3-6, 6-4, 7-6 (7/5).
Later Wednesday, 21-time Grand Slam champion Rafael Nadal sought to extend his perfect start to 2022 when he took on American Reilly Opelka for a quarter-final berth.
Nadal, 35 and currently ranked fourth in the world, is vying to become just the second player to start a season 18-0 on the ATP Tour (since 1990). Novak Djokovic has done it twice, starting 41-0 in 2011 and 26-0 in 2020.
Nadal's sizzing year has included a record-breaking 21st Grand Slam title at the Australian Open.
He went on to capture the title at Acapulco last month and is now gunning for a fourth Indian Wells crown.
The 24-year-old Opelka, at 2.11m one of the tallest players on the ATP Tour, is ranked a career-high 17th in the world and is seeking a fourth career Masters level quarter-final.
The winner of that match will face Nick Kyrgios for a place in the semi-finals.
The 26-year-old Australian advanced by walkover when scheduled opponent Jannik Sinner of Italy withdrew because of illness.
Kyrgios, playing his first tournament since winning the Australian Open men's doubles title in January with fellow Aussie Thanasi Kokkinakis, hasn't dropped a set so far this week. He toppled eighth-seeded Norwegian Casper Ruud 6-4, 6-4 in the third round.
Women's quarter-final action got underway on Wednesday, with third-seeded Iga Swiatek of Poland taking on American Madison Keys and former world number one Simona Halep facing Petra Martic.
Swiatek, 20, is coming off a title in Doha last month, has rallied from a set down in each of her matches this week, including an impressive fourth-round comeback against German world number one Angelique Kerber in which Swiatek trailed by a break in the final set.
Romania's Halep, a two-time Grand Slam champion who lifted the Indian Wells trophy in 2015, will be facing Martic for the first time since she beat the Croatian in the quarter-finals here in 2018.