U.S. stocks tanked in their worst two-day selloff since August. The financials sector slumped as major banks face regulatory uncertainty after the UK voted to exit the EU. Crude oil prices closed at their lowest level in a week as fears over the Brexit reached a crescendo. Those fears helped to strengthen the greenback which then deters foreign buyers for U.S.-produced oil. S&P cut the UK's sovereign credit rating to AA from AAA because of Friday's vote. The firm said the pro-exit result would lead to a less predictable and stable policy framework. Wynn Resorts (WYNN) - Get Report fell after delaying the opening of its Macau resort to August. The $4 billion resort had initially been projected to open in June. The project hit a snag as gambling revenue in the region suffers a protracted downturn. TheStreet's Keris Lahiff reports from Wall Street.