Athens on April 7 accepted in principle a tough set of new reform and tax measures in return for fresh cash to avert a possible debt default in July.
So-called bailout monitors had left Athens without a deal in March.
"The mission is returning to Athens today with the objective of concluding a staff level agreement as soon as possible," commission spokesman Margaritis Schinas told a daily briefing.
"Talks are to begin tomorrow and are expected to last several days," Schinas said.
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But the International Monetary Fund has so far refused to take part this time on the grounds that the targets were unrealistic and Athens' debt mountain unsustainable.
A senior IMF official said on Friday that it was "urgent" to reach a new agreement on the bailout programme, the latest payment of which has been held up by the row between Greece and its creditors.
Meanwhile, Brussels congratulated Greece for the 2016 primary surplus -- or budget surplus before debt repayments -- it registered in 2016, a key announcement for the reform talks.
Under the bailout, Greece needed to clock a primary surplus of 0.5 per cent of output in 2016, followed by 1.75 per cent this year and 3.5 per cent in 2018.