By Larry Fine
Clijsters sailed through an 18-minute opening set on a sun-kissed Arthur Ashe center court but fell behind 4-0 in the second set before roaring back to seize command.
The second-seeded Belgian ran off 12 straight points to pull within 4-3 and then broke in the 10th game and again in the last game to close out the match.
Clijsters won 78 percent of her first-serve points and registered three aces.
It was the 15th successive Open win for Clijsters, who last year scored an inspirational triumph in her return to grand slam tennis after taking two years off to start a family.
Clijsters began her current win streak by winning the 2005 U.S. championship, but missed the next year's tournament due to a wrist injury and then stepped away from the tennis circuit.
The 27-year-old Belgian treated the big center court crowd to a near-perfect opening set at Flushing Meadows.
Committing only two unforced errors on her crackling groundstrokes, Clijsters was rolling along until 104th-ranked Arn began finding the range on her serve, and errors crept into the defending champion's game.
"Beginning the second set she started going for a little bit more," explained Clijsters. "I kind of lost my positioning and my footing on court a little bit."
Clijsters sprayed four faulty forehands and three backhand errors in the second set but found her form in time to avoid a third set.
After Clijsters charged out to a 0-40 lead for triple match point in the 12th game, Arn dug deep and won the next two points before the Belgian ripped a backhand down the line to complete her victory.
Clijsters, who has won three tournaments this year, next meets Australian qualifier Sally Peers, who advanced with a 6-0 6-1 victory over Canada's Aleksandra Wozniak.
(Reporting by Larry Fine, Editing by Frank Pingue)