The turnaround at HSN Inc. continued in the first quarter with the TV shopping network reporting both a 9 percent sales increase and the first sales rebound at its ailing Cornerstone catalogs unit since the fourth quarter of 2007. Sales at Cornerstone rose 6 percent to $65 million, and its operating loss shrank to $2 million. Overall, the St. Petersbrug e-commerce retailer said net income leaped to $18 million, up from $3 million a year ago. Sales rose to $683 million, up from $629 million. HSN officials said the big sales gains of its past two quarters probably will moderate in the future as its sales performance starts being compared to stronger quarters in 2009. The first quarter that ends March 31 is usually the TV shopping network's weakest of the year.