Ferrari gave Mercedes a real run for their money at the Belgian Grand Prix and Merc team boss admits their rivals have "done a good job" with their package upgrades.
Spa-Francorchamps isn't usually a track that suits the Ferraris, but Sebastian Vettel kept the pressure on Lewis Hamilton during qualifying with the latter only getting pole position after setting a new lap record.
Vettel also kept Hamilton honest on Sunday and they found themselves neck-and-neck for most of the race, but the Mercedes driver somehow managed to hold off the charging German.
Wolff admitted after the race that Ferrari have caught up with them at tracks where they don't usually perform well, and the onus is now on Merc to respond.
"We were surprised. They have done a good job in bringing an upgrade package that works," he told Sky Sports F1.
"This is a track that shouldn't suit them, like Silverstone, and they were much closer than expected. We just have to keep our development scope steep and continue to bring bits on the car and deliver faultlessly."
He added: "We've not been good on high downforce circuits. Like Ferrari has caught us up at circuits like Spa, we need to catch up at circuits like Silverstone. It won't be a walk in the park."
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