A sign of spring? U.S. sales of BMW's Z4 nearly doubled in March. Source: BMW.

BMW Group (BAMXF 1.97%) said on Tuesday that its U.S. sales rose 8% in March, as a jump in sales for BMW-brand vehicles more than made up for a substantial drop in Mini sales.

BMW-brand sales rose 18.6% on the month, another sign that the U.S. luxury-vehicle market continues to be healthy. It was also enough to narrow archrival Mercedes-Benz's 2014 U.S sales lead to just a few hundred vehicles.

Balanced growth across BMW's luxury lineup
BMW said in a statement on Tuesday that last month was the BMW brand's best March ever. And unlike some other automakers -- notably Ford (F -3.01%) and Toyota (TM -0.54%) -- that have seen SUV sales increase at the apparent expense of car sales, BMW posted gains up and down its model line.

BMW's SUVs and crossovers (up 21.6%) did outperform BMW's cars (up 17.5%). But BMW's cars did well, with the company reporting especially big gains for the big 6 Series coupes and -- perhaps in a harbinger of spring -- its Z4 sports cars. But BMW's bread and butter, the 3 Series and 4 Series lines of compact sedans and coupes, was up a combined 14.2% over a strong year-ago result.

Year to date, U.S. sales for the BMW brand are up 11.5% -- a strong result, especially given the 5% gain posted by Mercedes-Benz and the 3% gain for Audi.

Mercedes and Audi aren't doing badly, but they lost ground in March
Mercedes took the U.S. luxury-car-sales crown away from BMW last year, and holding on to it in 2014 is a priority for corporate parent Daimler (MBGA.F 0.67%). Mercedes isn't doing badly: The brand saw U.S. sales rise 11.2% in March, ahead of the 6% gain posted by the overall U.S. market.

The story at Mercedes was similar to that at BMW: Solid sales of both cars and SUVs. Sales of the compact and midsize C- and E-Class sedans were strong, while the M-Class -- Mercedes' best-selling SUV line -- posted a 15.7% gain in March. 

Meanwhile, Audi has emerged as a global powerhouse and a major source of profits for parent Volkswagen Group (VWAGY -0.58%). But here in the U.S., it trails both of its German rivals -- as well as Lexus and Cadillac -- in total sales. 

It's not keeping up with either of its big global rivals here so far this year. Audi's U.S. sales were up 7.5% in March, outperforming the overall market but trailing the gains seen at both BMW and Mercedes-Benz. Like both its rivals, Audi saw strength in cars, with its A6 sedan up 26.7%, and in SUVs, with the plush (and expensive) Q7 posting a 45.8% gain.

The upshot: Luxury is strong, and BMW is taking full advantage
The U.S. market for luxury vehicles (at least, German-brand luxury vehicles) continues to be strong, as all three of the German makes outperformed the overall U.S. market in March. And BMW appears well-positioned to take full advantage at the moment.

But I suspect that Mercedes' boss, Daimler CEO Dieter Zetsche, won't relinquish the U.S. sales crown without a fight. How will Mercedes step it up in April? We'll find out.