Stocks were set to rise slightly at the open on Wednesday after data showed more jobs were created in the U.S. private sector last month than analysts had expected.

Trading will likely be volatile as a conviction that Spain will eventually request financial aid is offset by concern over a slowing Chinese economy.

Automatic Data Processing said 162,000 private jobs were created in September in the United States, more than the 143,000 expected by analysts, and down from a revised 189,000 in August.

The data was being closely watched ahead of the first of three presidential debates Wednesday night in Denver and a key government payrolls report on Friday.

"This is consistent with a moderate pace of job growth," said Scott Brown, chief economist at Raymond James in St. Petersburg, Florida.

"This is a big enough surprise that it might influence expectations for Friday's payroll report."

S&P 500 futures were up 1.6 points and slightly above fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures rose 12 points, and Nasdaq 100 futures added 6.5 points.

The Institute for Supply Management releases its September gauge on the services sector at 10:00 a.m. ET (1400 GMT). A Reuters survey forecast a reading of 53.2 versus 53.7 in August.

China's services sector weakened in September to its lowest since November 2010, as slow growth in manufacturing was seen feeding through to the rest of the economy.

European equities edged up and the euro steadied against the U.S. dollar, underpinned by a belief that Spain will eventually request financial aid, a step seen by some as required to resolve the euro zone's debt crisis.

Best Buy shares gained 3.4 percent in premarket trading as founder Richard Schulze and at least four private equity firms started examining its books, in early steps toward what could become an $11 billion buyout.

Shares of Family Dollar Stores rose 3 percent in premarket trading after the discount chain posted a higher quarterly profit.

Monsanto shares fell 3 percent in premarket trading after the agribusiness group posted a fourth-quarter loss during a seasonally sluggish sales period.

Google subsidiary Motorola Mobility has dropped a complaint of patent infringement against Apple without explanation.

(Additional reporting by Richard Leong; Editing by Bernadette Baum)