Emma Raducanu suffered a quick exit to Amanda Anisimova at Indian Wells, losing a third-round clash 6-1 6-1 in just 52 minutes.
Anisimova reached the Wimbledon and US Open finals last year and is the world No 6 and the level of her play was on full show against Raducanu.
After her split from coach Francisco Roig earlier this year, Raducanu had reunited with Mark Petchey on a day-to-day basis during this tournament.
While she had played well in her opening game, when she dispatched Anastasia Zakharova in straight sets, Raducanu struggled with Anisimova.
The American had Raducanu under pressure from the start as she broke the Briton's serve in the very first game.
With a double break Anisimova led 4-1 in quick time and didn't let Raducanu win another game in the set.
She closed out the first set with another break and to compound Raducanu's difficulties Anisimova broke again at the first opportunity in the second set.
Raducanu managed to claim a game but facing an ominous 4-1 deficit again in the second set, the Briton couldn't unearth a response. Raducanu suffered another break, which allowed Anisimova to serve out the match.
Raducanu said afterwards: "It was difficult to come close to putting my stamp on the match. That goes with playing Amanda - she is that sort of opponent who likes to put her stamp on it first.
"I have to take some positives. The first match here was better than a lot of matches I have been playing recently but a match like that [against Anisimova] is never easy to take."
Fourth seed Coco Gauff was forced to retire from her match with Alexandra Eala due to a "scary" injury to her left arm - although is hopeful she will be fit to play in the Miami Open from March 17.
Gauff, a two-time major champion, retired for just the second time in her career after trailing 6-2 2-0.
The American said: "It felt like a firework was going off inside of my arm and then my whole arm felt like it was on fire.
"We're going to figure out what it is [with an MRI on Monday] but based off the feeling, I'm being told that it's probably something nerve-related. I've never felt a sensation like this before.
"The good news is they don't think it's going to be a long-term type of situation, so I should be fine for Miami. We've just got to figure out exactly what it is and, I guess, how to prevent it in the future."
Top seed and 2025 runner-up Aryna Sabalenka cruised past Jaqueline Cristian 6-4 6-1 to reach the last-16 and will next face Naomi Osaka, who beat Camila Osorio 6-1 3-6 6-1.
It will be the first time Sabalenka and Osaka have crossed paths since their only previous match at the US Open in 2018, which Osaka won.
In the men's singles, second seed Jannik Sinner progressed after beating Denis Shapovalov 6-3 6-2, while fourth seed Alexander Zverev was taken to three sets before beating Brandon Nakashima 7-6 (7-2) 5-7 6-4.
Jack Draper and Novak Djokovic are among the men's players in action on Monday, taking on Franciso Cerundolo and Aleksandar Kovacevic respectively, and will play each other in the last-16 if they advance.
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