Lance Stroll was quick throughout the three segments of qualifying to end up fourth fastest while teammate Felipe Massa was ninth.

Williams has suffered with understeer at low speed, which in turn has hurt it in the rain and on circuits such as Monaco and Hungary.

Williams technical director Paddy Lowe could not explain the turn of speed and said the team set the car up in expectation for a dry race on Sunday.

"We set the car up for mainly dry conditions," he said. "I'm not going to pretend I have any idea why a car is strong or weak in the wet.

"I'm happy we found today the car was strong. It will be very interesting to study that in detail."

Massa said Williams compromised the set-up "very little" but it was "not really a big compromise".

He added: "I think maybe some others did the same because if you see the conditions today, it's not only one team that increased the downforce.

"We increase but very little so not really a big compromise. I don't know [why we were quick in the wet]. It's very difficult to get the right explanation.

"The rain today didn't disturb us. To understand 100 percent why, it's difficult to say."

Stroll will be promoted to second and Massa seventh as a result of grid penalties taken by Max Verstappen and Daniel Ricciardo for engine component changes.

Massa praised Stroll's lap, conceding he simply did not have the pace to beat his teammate in those conditions.

"Even if I had the perfect lap, it would have been maybe half a second quicker than I was but not Lance's lap time, so he did really a great job today," said Massa.