Red Bull Motorsport Advisor Helmut Marko has revealed Max Verstappen's brakes "deteriorated rapidly" during the United States Grand Prix.
The Dutchman secured a 15th win of the season and 50th of his F1 career from sixth on the grid at the Circuit of the Americas, coming out on top after a race-long strategic battle against McLaren's Lando Norris and Mercedes' Lewis Hamilton.
After reaching the front mid-race, Verstappen reported brake issues in an expletive-laden radio message to Race Engineer Gianpiero Lambiase and as the problems persisted, Hamilton eventually closed right in by the end of the race.
Addressing the issues, Marko told Sky Germany: "We had changed the brake pads and somehow they deteriorated rapidly during the race."
"That didn't give him the right feeling. Sometimes he braked predominantly with the front of the car, sometimes predominantly with the rear. It made it very difficult for him to drive at the limit, but he worked around those problems masterfully."
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Most difficult race of the year
Whilst Verstappen's dominance in the past two seasons has seen him make easy work of scything through the field from any starting position, his charge to victory at COTA was a more patient drive.
On the masterplan in place, Marko explained: "We told him to grab one [position] at the start and then take them one by one.
"From that perspective, we succeeded, but it was certainly the most difficult race of the year."