Meanwhile, Nvidia (NVDA) fell in sympathy as other artificial intelligence players plunged on earnings. And electric-car giant Tesla (TSLA) slipped on the stock market today amid industry delivery numbers for April.

Stocks on the Dow Jones index collectively climbed 1.2% shortly after Fed chair Powell spoke as several blue chips gained. But by the close, the index had faded to a 0.2% gain, or about 100 points. The Nasdaq, which had been up more than 1.5%, and the S&P 500 both closed 0.3% lower.

All three major indexes remain below their 50-day moving averages and were turned away at the 21-day moving average.

Small caps bucked the trend, however, with the Russell 2000 up 0.3%. The Innovator IBD 50 (FFTY) exchange traded fund trimmed its gain to 0.7% at the close of trading.

Volume was higher on the New York Stock Exchange and on the Nasdaq from Tuesday's totals, according to preliminary data. Advancers outnumbered decliners by about 3-to-2 on both main exchanges.

The yield on the benchmark 10-year Treasury note fell 9 basis points to 4.59%, a drop that accelerated once the Fed statement came out and Powell began his news conference.