Valtteri Bottas admits to being mystified at the loss of pace which saw the pole-man end the race in third.
Though the Finn led for the first 19 laps of the race, he was never able to build a lead of more than a couple of seconds, and consequently it came as no surprise when his teammate finally nailed him.
While initially able to keep pace with the Dutchman, despite a rare radio call from Toto Wolff, in the latter stages of the race the Finn fell away, amidst talk of an exhaust sensor issue.
Though he claimed the point for fastest lap, Bottas heads to Spain 37 points adrift of his teammate.
Asked to sum up his race, the Finn was in no doubt: "Disappointing," he replied.
"When you start from the pole position, you have only one target for the race and that is to win. It didn't happen today so I'm disappointed.
"I don't really know why in the first stint I didn't really have the pace," he admitted. "I mean, I felt everything in terms of the race start, the restart, everything was good from my side but I could see quite early on in the race that, with the mediums, I just didn't have pace like Lewis and Max had.
"I have no idea way," he sighed. "I don't have the explanation. It was better on the hard tyre and at some point I was catching Max and then I had an issue with one sensor that, I started to lose power and then I lost like five seconds to Max and that was it."
Asked if the car felt better following the switch to hards, he said: "Not on the first lap, it was really bad. But we know the warm-up today with the hard tyre was going to be tricky.
"Afterwards, once I got heat in the tyres, it was actually not bad and better than with the medium," he added. "Lots of things to look at, to analyse and learn from in the next two days before starting to focus for the next race."
Asked if it was unusual for Toto Wolff to urge him on over the radio, the Finn said: "No, it's not. There's been many times that he's, you know, opened the radio to say something.
"t's all supportive and it shows there's the support and the passion behind - and it never hurts. Obviously I'm always giving it every single bit I have on track. But yeah, it's good."
Toto Wolff subsequently explained the issue that hampered his driver in the latter stages of the race.
"The problem was we had a little gremlin in some engine software that we wanted to eradicate, and that did just the opposite," he admitted to Sky Sports. "That is something that we have to fix in our software.
"Based on our speed on the straights he might even have managed to pass (Verstappen)," said the Austrian of the issue.
"We had a good top speed on the straights today," he added. "The set-up we chose was the right one - a little to the detriment of downforce and drag - but quick on the straight. That worked well."
However, he refused to be drawn on whether the W12 is now the fastest car (again).
"The car was strong yesterday, which is a positive development," he said, "but it's hard to say today. I think both teams are on an equal footing, and you have to take P1 and P3 with the fastest lap."
Check out our Sunday gallery from Portimao, here.