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CHICAGO, June 16 (Reuters) - CME Group Inc CME.N, the world's largest derivatives exchange, on Monday cleared a key hurdle in its planned purchase of NYMEX Holdings Inc NMX.N when the deal got the blessing of the U.S. Department of Justice.

CME had said in January it planned to buy NYMEX, a big energy and metals market, and thus consolidate its stranglehold on the U.S. futures business.

Some industry watchers had expected more push-back from the DOJ to a deal that would give a single company a 95 percent share of the U.S. futures business.

On June 5, CME said it had resubmitted its pre-merger filing to give the Justice Department more time to review the transaction.

"We were confident that the Department of Justice would approve our combination," CME Group Executive Chairman Terry Duffy said in a statement.

The companies said the merger was likely to close in the fourth quarter, and generate some $60 million in cost synergies -- unchanged from earlier estimates.

The deal remains subject to approvals by regulators, shareholders of both companies and NYMEX members, as well as the satisfaction of various closing conditions.

At least 75 percent of NYMEX members must vote in favor of the purchase. Some are opposing the deal, insisting that CME sweeten the terms.