Audi made history last month. It is the first premium brand to rank as high as No. 2 in total European monthly sales. Audi outsold third-ranked Renault by 170 vehicles and topped No. 4 Ford by 1,578, according to data from industry group ACEA.

That good news, however, was offset by a lot of bad news at Audi’s sister brand, Volkswagen. August sales at VW brand were down 17 percent, which reduced its market share to 12.5 percent from 14.3 percent during the same month in 2012.

Despite the decline, VW brand remained No. 1 in European sales for the month, giving the VW Group the top two spots in the ranking for the first time.

The momentous occasion is probably not being celebrated in Wolfsburg because the sales numbers for VW brand are really troubling.

In August VW brand lost 17,522 sales in a market that was down by 35,501 units overall.

That means that VW brand accounted for nearly 50 percent of Europe’s overall sales decline last month.

What’s startling is that VW brand is slipping even thought executives at its main rivals told me that last month the automaker got even more aggressive with its discounting in Europe.

VW brand’s board member for accounting and controlling, Arno Antlitz, told workers on Tuesday that the company needs to undergo further belt-tightening over the coming months at all levels, in all departments, in all regions and at all plants. Those somber words make me wonder whether the VW car brand’s 34 percent first-half operating profit declined will get even worse when the full-year results are announced early next year.

The bottom line is that Audi’s stunning August performance was a rare bright sport for the VW Group, which suddenly seems a lot more vulnerable.