Gains in technology stocks helped the S&P 500 eke out another record on the last trading day of the month, while the Dow was dragged down by losses in industrial stocks.
Nvidia was up 2.13 percent and was among the top boosts to the S&P after Citigroup raised its price target on the stock.
Market's focus also remained firmly on President Donald Trump's tax plan and his ability to push it through Congress.
Trump's plan called for tax cuts for most Americans but drew criticism that the plan favors business and the rich and could add trillions of dollars to the deficit.
"For the market, the most important thing is tax cuts for the corporations and that, most likely, will not be tampered with," said Peter Cardillo, chief market economist at First Standard Financial in New York.
"But any disappointment going forward would certainly take the wind out of this market as it has rallied on hopes of cuts."
The dollar was on track for its biggest weekly rise in 2017 after Trump's tax plan, while the three major Wall Street indexes were set to lock in gains for the month and the quarter.
At 9:39 a.m. ET (1339 GMT), the Dow Jones Industrial Average was down 39.44 points, or 0.18 percent, at 22,341.76, the S&P 500 was up 0.75 points, or 0.03 percent, at 2,510.81 and the Nasdaq Composite was up 15.91 points, or 0.25 percent, at 6,469.36.
Data earlier in the day showed cooling consumer spending in August and slowing pace of annual inflation growth.
Seven of the 11 major S&P sectors were lower, led by a 0.51 percent loss in the energy index. Oil giants Exxon and Chevron were the biggest drags on the S&P.
Technology index rose 0.41 percent.
Alphabet's 1.12 percent rise and Amazon's 0.6 percent gains propped up the Nasdaq.
KB Home jumped about 6 percent after the homebuilder's profit and revenue came above estimates, prompting a slew of price-target raises.
Advancing issues outnumbered decliners on the NYSE by 1,357 to 1,137. On the Nasdaq, 1,391 issues rose and 892 fell.