A domestic brand surge and an easy comparison against last year vaulted September new-vehicle sales 35 percent higher at AutoNation Inc., the country’s largest retailer.

AutoNation reported today that it sold 18,040 new vehicles at retail last month. Domestic brand sales rose 54 percent to 5,353, import sales rose 34 percent to 9,558 vehicles, and premium luxury brand sales rose 14 percent to 3,129.

“It was the easiest comparison of my career,” AutoNation CEO Mike Jackson said during an interview this morning with CNBC. “I’ve been looking forward to [comparing] against September of last year, when we were sold out due to cash for clunkers.”

For the entire third quarter, AutoNation posted retail new-vehicle sales of 56,340, a 3 percent increase over the clunkers-aided third quarter of 2009.

Chrysler Group brands led AutoNation’s September increase, with sales up 64 percent. The new Jeep Grand Cherokee is an “absolute hit,” Jackson said on CNBC. “The resurgence of the domestics continues.”

AutoNation’s pickup sales rose 50 percent in September. Businesses are buying replacements after postponing such purchases during the downturn.

Jackson said on CNBC that sales this summer were strongly linked to holiday promotions: “It was all about Memorial Day, Labor Day and the Fourth of July -- and Labor Day was absolutely spectacular.”