A "very sharp stone" pierced one of Rene Rast's tyres in parc ferme, forcing Audi into 'mixing' his tyres for an 'imbalanced' first stint in the DTM Brands Hatch race.
Rast won Sunday's race at Brands Hatch after recovering from losing his pole position to Loic Duval at the start, and he later held off title rival and Audi stablemate Nico Muller for victory.
But Rast's 10-lap first stint was not completed with his "best set" of tyres used during qualifying, and it forced the Audi driver to carefully manage his tyres over the first stint.
Under parc ferme conditions, DTM teams are allowed to change their allocation of tyres, and the setback forced Audi to mix and match his set for the start of the race.
Audi motorsport boss Dieter Gass told Autosport: "In parc ferme, he [Rast] went over a very sharp stone.
"When you enter parc ferme with a hot tyre, the rubber is extremely soft and the stone really went into the tyre, and we couldn't use it anymore."
Gass added that he believes Rast had driven cautiously after losing a nailed-on victory at Assen due to excessive tyre degradation that forced him into a late second stop.
"The pace [of Rast] was OK," said Gass. "I haven't spoken to him yet, but I think the experience he had with Assen, he was trying not to over-stress the tyres.
"It looked an easy win in Assen until the tyres went, and today he did everything he could."
Speaking in the post-race press conference, Rast said: "I couldn't use the qualifying set, which was unfortunate because it was the best set we had."
Expanding on the situation to Autosport, Rast added: "We actually had a mix of sets.
"I had quite an imbalance from left to right, [the lefts] had five to six laps left and the right-hand side had much more [tyre life] left.
"[It] wasn't easy to get the balance into the window and the first stint. In the end, the second stint, we had a good tyre set.
"The second was not influenced, just the first set. But I felt the first stint was not easy to be quick with the first set."
Audi is believed to have a stronger engine in terms of power and reliability compared to BMW.
But Audi locking out the top eight positions on the grid with all eight Audis in Sunday's qualifying session surprised BMW, a day after Marco Wittmann put his M4 DTM on pole for the opener.
Asked by Autosport if Audi understood why it had such an advantage, Gass said: "No.
"Qualifying was bizarre today because I was looking at the timing screens after the first runs - 'wow, what's going on here?'.
"I was sceptical about the situation, 'are they saving tyres? What's going on?'
"I expected an attack [from BMW] in the second run, which didn't happen.
"I think Marco [Wittmann] didn't have the best of laps like [he did] yesterday, others like Philipp [Eng], they improved their time compared to yesterday.
"We just had a very good qualifying, everybody had good laps."