Leaders Lincoln ran out 1-0 winners over county rivals Grimsby in the division's early kick-off at Sincil Bank.
Full-back Harry Toffolo's strike proved the difference between the two sides in what was a relatively tame Lincolnshire derby, despite the number of cards shown by referee Mike Dean.
Michael O'Connor's 12th minute corner was cleared as far as Toffolo, who lashed home a 20-yard volley to put the hosts ahead.
Nine minutes later Lee Frecklington latched onto a through ball from Neal Eardley that caught out the visiting defence, but his shot was deflected behind for a corner.
At the other end a mistake by Lincoln debutant Cian Bolger allowed Jake Hessenthaler to capitalise and find Sebastian Ring. The full-back found Elliott Embleton inside the penalty area, but after neat footwork he scuffed his shot wide.
After the break Shay McCartan thought he had doubled the Imps' lead, but referee Dean spotted John Akinde's foul on Ring.
Grimsby's misery was compounded 14 minutes from time when goalkeeper James McKeown received his marching orders for a foul on the on-rushing debutant Danny Rowe 35 yards from goal.