Joe Braithwaite’s goal late in the first-half came after two early strikes from Nomads that ultimately proved enough for the win as they continue their pursuit of promotion, having a large number of games in hand on those above them.
And Greens player-boss Tom Ward felt the slow start cost his side dearly.
He said: “We probably gave them too much respect in the first 20-25 minutes and got punished twice for it.
"But from then on we grouped together and it was a case of staying in the game and not getting turned over.
"Obviously scoring just before half-time changed the game for us and we came out much more positive in the second-half – they had to defend a lot more and you could tell with how they celebrated at the end that they were really happy to get through it.
"Their keeper had to make a couple of great saves in the second-half and we could have got something out of the game.
"That’s the small margins and probably why they’ll go on and win this league so good luck to them.
"We had a few things go against us including Joe Smith pulling up in the warm-up but we had a young side that went toe-to-toe with probably the best team in the league and we learned a lot and it should put us in good stead.”
The result saw Sleaford slip below Anstey in the table who moved into fourth, the Greens still only three points off second place with leaders Loughborough Students top and 14 points clear, although Nomads could overtake them if they win all of their six games in hand.
Sleaford now prepare to travel to Derbyshire to face seventh-placed Heanor Town on Saturday, with Ward hoping to have several key players returning to the side, including himself having only played for a few minutes late on up front against Anstey as his side chased an equaliser.