An initial selloff took the S&P 500 to its 100-day moving average, but by the last hour of trading, the benchmark index was back near the unchanged mark. Sectors posted mixed performances, with four of the S&P's 10 industry sectors ending with gains.
The S&P 500 telecom services sector slipped 1.3 percent and was the worst-performing industry, with AT&T and Verizon down on news that Sprint, facing regulatory resistance, gave up its bid for T-Mobile.
Investors have been expecting a correction, but selloffs this year have generally been brief.
"We've had a lot of forces pushing the markets, whether it's earnings season, employment numbers or geopolitical concerns, but I think if people were really concerned about an invasion in Ukraine or the Middle East, you would see more than a 2 or 3 percent selloff," said Gary Flam, portfolio manager at Bel Air Investment Advisors in Los Angeles.
NATO reported that Russia has around 20,000 combat-ready troops on the eastern border of Ukraine that it could use to invade. Further souring the mood, Russian President Vladimir Putin announced Moscow's biggest economic response to Western sanctions so far.
The Dow Jones industrial average rose 13.87 points, or 0.08 percent, to 16,443.34. The S&P 500 was up 0.03 point, or 0 percent, to 1,920.24, and the Nasdaq Composite added 2.22 points, or 0.05 percent, to 4,355.05.
Walgreen Co shares fell 14.3 percent to $59.21 after the largest U.S. drug retailer it said it would not use a full takeover of Europe's biggest pharmacy chain, Alliance Boots, to domicile overseas - a move that would shield Walgreen from U.S. taxes.
On the upside, Molson Coors Brewing Company gained 5.8 percent to $71.08 after better-than-expected earnings, helping lead consumer staples companies higher.
Twenty-First Century Fox Corp was another winner, its shares up 3.3 percent to $32.33, a day after the company pulled its $80 billion offer to buy Time Warner Inc. Time Warner slid 12.9 percent to $74.24.
About 6.4 billion shares traded on all U.S. platforms, according to BATS exchange data, compared with the five-day average of 6.8 billion.
Advancing issues outnumbered declining ones on the NYSE by 1,804 to 1,222, for a 1.48-to-1 ratio on the upside. On the Nasdaq, 1,597 issues rose and 1,056 fell for a 1.51-to-1 ratio favoring advancers.