A sell-off in top holding Apple (NasdaqGS: AAPL) pulled down the Nasdaq-100 PowerShares QQQ (NasdaqGM: QQQ) on Wednesday, one day after the popular ETF notched its highest price level since 2000.

QQQ has been outperforming the S&P 500 for nearly two months but now the Nasdaq-100 ETF is starting to lag the market in what could be an important emerging trend.

“This morning’s down open on the Nasdaq-100 has printed an island reversal on the chart, far from bullish bearing in mind that the index made a new decade high yesterday. This area has been leading strongly on a relative basis since late July but this fresh weakness raises a red flag,” said Investors Intelligence technical analyst Tarquin Coe.

“The Powershares QQQ ETF also shows a bearish momentum divergence with yesterday’s high and today’s slide. With the relative uptrend off the July low now broken, the weakness is not going to be short-lived,” he wrote in a newsletter Wednesday.

QQQ was in the red Wednesday while the Dow and S&P 500 both traded higher.

Apple shares were down 5% on Wednesday as Wall Street analysts were left disappointed by the unveiling of the company’s latest iPhones.

Apple is the largest holding in the tech-heavy QQQ at 13% of the portfolio. [Apple Weighs on Nasdaq ETF]

PowerShares QQQ

Full disclosure: Tom Lydon’s clients own AAPL and QQQ.