Comcast Corp. (CMCSA), the largest U.S. cable operator, Wednesday posted a third quarter profit on better-than-expected gains in high-speed Internet customers and raised its full-year outlook for subscriber growth.

But profit was hurt by the cost of courting new customers in the face of stiff competition from satellite television operators and telephone companies.

The Philadelphia-based company added 549,100 net new high speed Internet customers in the third quarter, well ahead of even the most aggressive Wall Street estimates of about 475,000.

Third-quarter net income was $220 million, or 10 cents a share. A year earlier, net earnings were $3.18 billion, or $1.41 a share, including a one-time gain of $3.29 billion, or $1.48 a share, from the sale of its stake in the QVC shopping channel (search).

Comcast spent about $30 million in the quarter to court the back-to-school college students, but added 100,000 more customers than it expected. These customers are expected to generate about $50 million in revenue per year.

"That's a pretty good trade-off, one we'd make again," said Comcast chief operating officer Steve Burke.

The company also managed to add new customers without heavy discounting, said Craig Moffett, an analyst at Sanford C. Bernstein.

Comcast raised its target for full-year high-speed subscriber net additions to a range of 1.6 million to 1.7 million, up from an earlier forecast of 1.5 million to 1.6 million.

Revenue rose 12 percent to $5.09 billion from $4.55 billion a year earlier.

Comcast reported average monthly revenue per user of $42.91 in the third quarter, ahead of Moffett's estimates but slightly below the second quarter's $43.52.

Cable operators have had to defend their turf against satellite television competitors DirecTV Group (DTV) and EchoStar Communications Corp. (DISH), which attracted more video subscribers than expected in the second quarter.

"The company has been trying to figure out the best balance between customer and financial growth," said Thomas Eagan, an analyst at Oppenheimer & Co. In the second quarter, Comcast focused on maintaining profits, but lost subscribers to aggressive satellite TV operators.

Comcast's strong customer growth in the third quarter eased some of the worries investors had over competitive forces, but the cable sector is not out of the woods. "Concerns about satellite competition are real and they're going to persist," Moffett said.

Comcast added 8,500 net new basic cable subscribers in the third quarter, reversing a net loss of 96,000 subscribers in the second quarter. But the third-quarter figure fell shy of Wall Street projections of about 15,000 net additions.

It ended the quarter with 21.5 million basic cable subscribers, essentially the same level as a year ago.

It expects basic cable subscribers to remain at 21.5 million, which implies it expects no net additions in the fourth quarter.

Shares of Comcast rose 33 cents to $29.25 in morning trading on the Nasdaq.