All eyes are on Goldman Sachs , which announces earnings tomorrow. What goosed the stock…and then the banking sector and then the entire market today? Meredith Whitney’s upgrade.

It mattered–and helped send Goldman up nearly 5% to $149–because the famously bearish financial-services analyst, who helped bring down Citigroup and the banking sector two years ago, has been negative ever since. She announced her upgrade of Goldman at 2:24 a.m. At least that’s when the email from her company, Meredith Whitney Advisory Group, popped into my inbox this morning. This is Whitney’s first upgrade since she broke away from Oppenheimer in February to go on her own. It’s also her only “Buy” rating among eight stocks she follows.

So yes, Meredith Whitney finally turned…on one stock only. Don’t dare call her a bull on the market. She says in today’s Goldman report that her positive outlook “is deeply rooted in our sustained bearish stance on the U.S. economy and state of U.S. financials at large.”

She likes Goldman because she’s predicting “a tsunami of debt issuance” from federal, state, and local governments to shore woefully underfunded budgets. That, plus a surge in corporate debt issuance (to at least 60% of peak cycle levels, she says) will benefit Goldman, which along with Morgan Stanley is the last Wall Street giant standing. Survival of the fittest, precisely. The weak fall and the strong get stronger.

As for Whitney, she’s showing her muscle. Last week here at Fortune, we were talking about her as we began to assess the crop of candidates for this year’s Fortune Most Powerful Women in Business list, due out in mid-September. Last year Whitney ranked No. 35 on the list. We were wondering if she’s still got her mojo. Guess she does.

P.S. Whitney has sells on three stocks: Wells Fargo , Capital One , and Citigroup .