NEW YORK (TheStreet) -- Stocks may have closed the day lower, but benchmark indexes did manage to generate positive returns for the month, a surprise for those who subscribe to the strategy of "sell in May and go away."

The S&P 500 closed with monthly gains of 1.1%, its best monthly gain since February. The Dow Jones Industrial Average added 1%, and the Nasdaq climbed 2.6%.

Those gains weren't felt on Friday, a session pressured by a downward first-quarter GDP revision and nerves ahead of next week's jobs report for May. The S&P 500 fell 0.63%, the Dow declined 0.63%, and the Nasdaq slid 0.55%. Economists hope to see continued strength in the labor market, proof that March's disappointing number was an aberration in a weak first quarter.

The data "will go a long way toward helping validate if the Federal Reserve is correct in its assumption that a lot of the things that negatively impacted the first quarter were transitory," said Eric Wiegand, senior portfolio manager at U.S. Bank, in a call.

Economists expect the economy to add 210,000 jobs in May with the unemployment rate remaining unchanged at 5.4%. Hourly earnings are forecast to increase 0.2% month on month. The Labor Department will release the data on Friday, June 5.

First-quarter gross domestic product, originally seen up 0.2%, was revised down to negative 0.7% in a second estimate. The contraction was slightly narrower than economists had expected, though marked a stark reminder of how bad economic growth truly was at the start of the year.

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