Singh ran through the Mumbai batting line up to return with impressive figures of 6-73 as the opposition was skittled out in just 58 overs at the Mumbai Cricket Association's Bandra Kurla Complex ground here.
In reply, Delhi made a flying start and ended the day at 140/1, just 90 runs adrift of the hosts' first innings total.
Delhi openers Hiten Dalal (67) and Anuj Rawat (68 not out) notched up fifties. At stumps, Rawat had the company of Yash Sehrawat (1 not out).
One down Vaidik Murkar (26) showed some resistance but failed to convert his start into a big score.
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Others A Sardesai (0), Siddharth Akre (4), S Mulani (19), Sairaj Patil (4) and Khiraz Dafedar (4) fell cheaply, giving Delhi the advantage on the first day of the four-day match.
Karsh Kothari remained unbeaten on 19.
Singh was rewarded for bowling in the right areas and was ably supported by Shivank Vashisth (2-46), Lalit Yadav (1-19) and Gourav Kumar (1-37).