Ford Focus sales caught fire in September, skyrocketing 91.0% vs. year-ago to 19,697, according to WardsAuto data.

Several factors contributed to the strong month, including inventory constraints of other popular Ford vehicles, says Ken Czubay, Ford vice president-U.S. marketing.

Deliveries of the Fusion midsize sedan plunged 38.3% compared with like-2011 to 11,685 units. Much of the decline resulted from the sell-down of the current model and buildup of all-new ’13 models just now arriving on dealership lots, Czubay says.

“With the depletion of Fusion, there were people who went to Focus,” he tells analysts and journalists in a conference call. “It’s just a great value proposition, and that’s the expected sales rate (for Focus).”

Although Ford is targeting Focus sales at about 20,000 units per month, demand could slow as inventories of the ’13 Fusion build and the new C-Max hybrid-electric vehicle arrives on dealer lots, Czubay says.

The Focus’ September tally helped lead to Ford’s best small-car sales result since 2002. The auto maker says in the last five years it has increased its share in the small-car segment to 10% from 6%, with deliveries in California, the largest U.S. auto market, rising 68%.

The all-new ’13 Escape cross/utility vehicle, which has been plagued by recalls, including one announced today due to a potential fire risk, had a good showing in September, with deliveries rising 17.6% to 23,125.

The Escape’s performance came despite low inventories and a decline in the overall small CUV segment, Czubay says. Half of ’13 Escape sales were conquests and 60% of overall sales were of high-trim levels.

“When you launch a new product it’s (typically) a richer mix,” Czubay says. “It’s too early to tell, but dealers are saying consumers are dazzled by the technology” on high-trim-level Escapes.

The popularity of the new Escape may have been detrimental to the midsize Edge CUV, sales of which fell 7.7% vs. year-ago to 10,771 units. But Czubay says the larger model isn’t being cannibalized by the small one.

“Escape has always been a good performer, and we expect it to do well,” he says. “But we’re not seeing too much migration from Edge to Escape.”

The stellar performance by the Focus and solid showing for the Escape were not enough to give Ford’s overall September sales a boost. Total deliveries slid a fractional 0.8% on a daily rate basis to 170,978 vehicles, against and industry expected to record double-digit gains. There were 25 selling days both this year and last.

Most models posted declines, including the Mustang (down 12.1%), Flex (off 27.1%) and F-Series (down 0.9%).

Czubay does not address Mustang or Flex in the conference call, but notes F-150 deliveries started out slow but built momentum as the month progressed.

Some of Ford’s lower-volume vehicles performed well in September, including the Transit Connect small commercial vehicle, which was up 15.4% vs. year-ago to 3,013 units, and the Lincoln Navigator, up 28.1% to 846.

Ford’s fleet mix last month was 26%. Of that, 13% went to commercial buyers, 5% to government agencies and 8% to daily rental companies.

The auto maker ended the month with 450,000 light vehicles in stock, including 114,000 cars, 225,000 trucks and 111,000 utility vehicles.