I guess the number 13 proved to be unlucky for Staples (NASDAQ:SPLS), the nation's leading office supply retailer. After stringing together 12 consecutive quarters of 20% or better earnings growth, the company fell just short of extending that impressive streak. Fourth-quarter earnings, released this morning, rose to $0.50 from $0.42 a year ago -- a 19% increase. For the year, net income rose 45% to $708.4 million, or $1.40 per share.

The company posted solid gains on the top line as well, as revenues climbed 13% during the quarter to $4.1 billion. There was an 8.4% increase in North American retail sales (which represents more than half of total revenues), driven by a solid 4% gain in same-store sales. Growth was even more robust at Staples' other two segments: Delivery sales were up 18.5%, and international operations (which have recently been expanded to 21 countries) reported a 22.2% increase.

Staples has played king of the office supply hill for a while now, but Office Depot (NYSE:ODP) is mounting a renewed effort to retake the summit. Earlier this month, the former leader posted a 4% improvement in fourth-quarter comps -- the sharpest rise in nearly five years. Of course, that claim is easy to make, considering Office Depot spent the majority of that period mired in a 16-quarter slump during which same-store sales went nowhere but down.

After years of relative quiet (only 12 new units added from 2000 to 2003) on the expansion front, Office Depot has finally taken aim squarely at Staples' home turf in New England, where it opened a healthy percentage of its 70 new stores last year. OfficeMax (NYSE:OMX) is also trying to make some inroads as it expands its store base. Neither of Staples' primary rivals has much direction from the top these days, though. Office Depot's CEO resigned abruptly several months ago, and OfficeMax has cleaned house in the wake of a billing scandal.

While increased competition is not exactly welcome news, it is hardly alarming. Staples holds a commanding lead, with nearly 1,700 superstores. Furthermore, today's results only strengthen the company's leadership position: Inventory turns are improving, industry-leading operating margins are expanding, its delivery business reported double-digit growth across all three divisions, and new private-label merchandise and copy center initiatives are taking hold.

Not only are earnings forecast to grow 15% to 18% this year, but with free cash flows swelling to a record $844 million, the company's dividend has also been bumped up by 25%. Numbers like that indicate that management is equally upbeat about Staples' chances this year.

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Fool contributor Nathan Slaughter owns none of the companies mentioned, though he does own the movie "Office Space."