The hosts started brightly and James Walshaw forced King into his first save of the afternoon as the goalkeeper palmed away his effort.
King denied the Scarborough striker again moments later this time saving at his feet as the forward tried to take the ball around the goalkeeper.
Rangers tried to respond and Andy Haworth saw his shot fall into the side-netting on 21 minutes.
However, moments later Scarborough took the lead with Kian Spence sliding in a cross for Michael Coulson to net the opener.
It could have been two before the break but Chris Dawson saw his effort denied by King.
After the interval the momentum of the tie changed and Brad Grayson fired the Boro level with a rifled effort across the goalkeeper.
King was forced into a host of further saves as the second half wore and Rangers almost stole the points at the death only for Sam Coulson to rattle the post.