Felipe Massa may have completed a mammoth 168 laps and topped the timesheets on the first day of the second week of Formula One pre-season testing, but the Brazilian insists Williams are still off the pace of Mercedes and Ferrari.
Massa enjoyed a profitable day on Tuesday as he racked up the more laps than 11 of the other 12 drivers in action - with only Sebastian Vettel able to match him in his Ferrari.
The 35-year-old - who returned to Williams for 2017 following Valtteri Bottas' switch to Mercedes, despite retiring at the end of last season - recorded the quickest time on his supersoft tyres, Massa stopping the clock at one minute 19.726 seconds.
That was nearly two tenths quicker than Red Bull's Daniel Ricciardo and Vettel, while the Mercedes duo Lewis Hamilton and Valtteri Bottas were seven tenths and 1.1 seconds back respectively.
Despite the pace and longevity he showed in Barcelona, Massa urged caution ahead of the Australian Grand Prix later this month, when he does not expect to be challenging for victory.
"I am so happy for the day, I don't remember before doing a day with 168 laps in my career!" he told Sky Sports News.
"It was a lot of laps and l can feel it a bit on my body, but l am good. I feel in good shape for the new season.
"[But] I don't think we are on the same level as Mercedes.
"Mercedes have already shown incredible speed. But if we can fight for podiums then that will be a great job. We will see where we are in Australia."
Ricciardo also expects to see more from Mercedes in Melbourne, plus improvements from Ferrari and his own Red Bull.
"We definitely feel we still can get more out of the car, but probably everyone can," said the Australian, as quoted by Autosport.
"Hopefully not Williams - hopefully that was their best today! [Tuesday]
"I think Ferrari and Mercedes can still get more out of theirs. Even though Williams didn't run much last week, today they did a good run.
"I actually think they looked quite good. It's going to be interesting. Melbourne will be a nice little story."