Goalscorer Hartson was delighted to have broken his scoring duck for the season, but he also admitted that Klos had looked unbeatable before his deflected winner.
Stefan Klos kept Rangers in front when Martyn Corrigan met Steven Hammell's free kick with a header from six yards only for the German to block the effort with his chest.
Stefan Klos was out to make a point after being frozen out of the German international squad and made a great save to block at the feet of Stuttgart's Alexander Hleb.
Hibs pushed forward from the start and midfielder Ian Murray should have done better than scuff his shot wide after goalkeeper Stefan Klos's punch fell nicely for him at the edge of the box.