Carlos Sainz departed Shanghai utterly perplexed, grappling with what he described as "one of the strangest drops in performance I've had in my career."
After losing his Ferrari drive and opting for a move lower down the grid, the 30-year-old Spaniard initially shone in his new Williams during early outings.
A crash marred his start in the rain-soaked Australian season opener, but the sprint and grand prix in Shanghai left Sainz stunned by his lack of pace.
"I'm a bit confused," the four-time grand prix winner told DAZN.
"I was very fast in the (2024) Abu Dhabi tests, I was very fast in Bahrain, and for some reason, all the pace I had in the tests has vanished in one fell swoop in this first real race with the team," Sainz remarked in China on Sunday.
"There is a lot to analyse and we need these ten days to analyse everything calmly to see what we can do better," he continued, alluding to the brief window before action begins at Suzuka.
"Ten days are enough, I'm sure we'll find something and come back stronger. But here, we've been going very slowly," Sainz admitted.
Compounding his frustration, teammate Alex Albon has avoided the same woes.
"From yesterday (Saturday) to today, we changed the setup of both cars a lot, and it worked for Alex and he was able to finish in the points," said the Spaniard. "For me, I continued to struggle a lot with the front graining, opening up the tyres a lot on both the medium and hard tyres, and I haven't been going fast, so there's a lot to analyse.
"This was my first real test with the car, and clearly it didn't work out."
Sainz remains optimistic that Williams can resolve the issue swiftly, pointing to Haas as an example. While Haas bosses had been glum about a "fundamental" flaw after Australia, he noted, "suddenly, a bit like last year, they seem to have improved a lot."
Haas newcomer Esteban Ocon echoed that sentiment, explaining how rapidly the American outfit tackled its earlier troubles.
"Everyone is happy," he told Canal Plus. "We managed to turn the situation around in a week. It shows that we know where we're going."
