S.D. Codified Laws § 21-41-25

The court may, in its discretion and upon such terms as may be just, at any time within two years after the entry of judgment, relieve a defendant in such action from the judgment, if taken against him through his mistake, inadvertence, surprise, or excusable neglect, and allow such party to defend the action, but the defense, if successful, shall be without prejudice to the rights of a purchaser or encumbrancer in good faith of the premises from the plaintiff after the entry of such judgment, and before the making of the order permitting such defendant to defend.