The Dow Jones Industrial Average slipped a scant 4.76 points (0.03 percent) to 16,264.23.
The S&P 500, a broad measure of the markets, shed 3.52 (0.19 percent) at 1,849.04, while the tech-rich Nasdaq Composite Index was the worst performer, tumbling 22.35 (0.54 percent) to 4,151.23.
Markets spent the better part of the day in negative territory, extending Wednesday's losses.
Trade was choppy after data showed a drop in first-time claims for US unemployment benefits last week, an upward revision to US fourth-quarter economic growth to an annual rate of 2.6 percent, and a steeper than expected fall in pending home sales to the lowest level since October 2011.
IBM was the Dow's biggest drag, falling 1.5 percent, followed by Cisco, down 1.3 percent.
Citigroup plunged 5.4 percent in the wake of the Federal Reserve's rejection of its share buyback and dividend increase plans due to weakness in its results in stress tests.
Microsoft weighed on the Nasdaq, losing 1.2 percent. The software giant released a version of its popular Office suite for rival Apple's iPad tablet, a landmark move toward making its applications run across all platforms. Heavyweight Apple fell 0.4 percent.
Facebook reversed hefty earlier losses and ended almost 1.0 percent higher. The social media company shed 6.9 percent on Wednesday, as investors question its $2 billion deal to buy virtual reality company Oculus.
Candy Crush maker King Digital sank for a second day after the British firm's IPO, losing 2.7 percent to $18.49, compared to the IPO price of $22.50.
Yahoo added 0.4 percent. Yahoo Japan said it would buy almost all of domestic telecom company eAccess from its parent Softbank Corp. in a deal valued at around $3.2 billion.
Twitter leaped 4.3 percent. The company on Wednesday added Facebook-style photo tagging and bumped up the number of images that iPhone users can share in a single post.
Bond prices rose. The yield on the 10-year Treasury fell to 2.67 percent from 2.70 percent on Wednesday, while the 30-year yield dropped to 3.51 percent from 3.55 percent. Bond prices and yields move inversely.