Wall Street's main indexes opened flat to slightly higher in Tuesday's shortened trading session, with U.S. stocks entering a historically strong period before rounding off their second consecutive year of gains.

The S&P 500 posted two new 52-week highs and one new low, while the Nasdaq Composite recorded 26 new highs and 43 new lows.

Stocks shook off a choppy start to finish higher Monday, as Wall Street kicked off a holiday-shortened week. The S&P 500 ended 0.7% higher after having been down 0.5% in the early going. The Dow Jones Industrial Average also recovered from an early slide to eke out a 0.2% gain. The tech-heavy Nasdaq composite rose 1%.