(This Dec. 15 story has been corrected to fix the name of the reporter in the signoff line at the end of story)

By Carolina Mandl and Summer Zhen

NEW YORK/HONG KONG (Reuters) - Global equities long/short hedge funds' bets against U.S. stocks got squeezed in the last two days after U.S. bond yields slid, two investment banks said in notes that were sent to hedge fund clients and obtained by Reuters.

Both Goldman Sachs and Jefferies said long/short hedge funds, which take positions betting stocks will rise and fall, got hit hard after Fed Chair Jerome Powell on Wednesday indicated that the U.S. central bank's historic tightening of monetary policy was likely over.

That remark, made in a press conference after the end of a two-day Fed policy meeting, sparked a rally in stocks, with the up 1.6% over the past two days. On Friday, the index was largely muted. The yield on U.S. was little changed at 3.8998% on Friday, after sinking to its lowest level since July on the Fed's dovish pivot.

Jefferies' trading desk said that long/short hedge funds on Wednesday and Thursday had their "second-worst two-day move ever," as long positions outperformed short bets. The investment bank analyzed a metric called the long/short spread that shows the performance of long versus short trades.

Goldman Sachs said systematic equities long/short hedge funds on Thursday had their worst day in roughly eight years. "Negative performance (was) driven by (a) squeeze in crowded shorts, momentum sell-off and rally in high beta and high volatility stocks," Marco Laicini, a managing director at Goldman, said in the note.

The investment bank's global markets team said systematic long/short funds, based on a computer-driven strategy, were down 2.8% on Thursday, the worst single day since at least January 2016.

The Goldman note pointed to "crowded trades (mainly shorts), momentum and volatility among key negative drivers," adding that there was high volatility. Still, systematic funds are up roughly 13% on a year-to-date basis.

Goldman and Jefferies did not immediately comment on their notes, details of which have not previously been published.

Jefferies told its clients that the pain was not limited to long/short hedge funds, with "lots of frustrations and pain on the sidelines from systematic, macro, fundamental long/short managers alike."