The visitors started the brighter of the two sides, with Reece Styche having a low strike well kept out by Daniel Lloyd-Weston, but Southport soon came into the match with Richard Brodie driving just wide of the post.
The home side broke the deadlock on 25 minutes when Joe Connor found himself in the right place at the right time to divert the ball from close range from a corner.
The visitors responded well to falling behind, but after Craig Reid had seen his effort saved by Lloyd-Weston, Southport held on to maintain a slender advantage at the break.
That lead was almost extended in the opening moments of the second half when Scott Kay got on the end of a cross, but his header hit the post before being cleared by the Kidderminster defence.
Southport had perhaps expected an offensive response from their opponents, but they were able to stifle the fourth-placed side before Harriers finally made progress with a number of set pieces as the game entered the final 15 minutes.
The hosts were reduced to 10 men with eight minutes remaining when Brodie was dismissed for a second bookable offence, and Kidderminster almost took full advantage through Cheyenne Dunkley but his header cleared the crossbar.
Aman Verma also went close with a free kick, but Southport held on to condemn Kidderminster to their first setback of the campaign.