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In this first paper of the series we describe our project to calibrate thedistance determination method based on early-type binary systems. The finalobjective is to measure accurate, geometrical distances to galaxies beyond theMagellanic Clouds with a precision of 2%. We start with the analysis of twoearly-type systems for which we have collected all the required spectroscopicand photometric data. Apart from catalog publications, these systems have notbeen studied yet, and it is the first time the modeling of light and radialvelocity curves is performed for them. From the analysis we obtained precisephysical parameters of the components, including the masses measured withprecision of 0.6-1% and radii with precision of 0.4-3%. For one system wedetermined the $(V-K)$ color and estimated the distance using the bolometricflux scaling method (DM=18.47 $\pm$ 0.15 mag), which agrees well with ouraccurate determination of the distance to the LMC from late-type giants. Forthe same system we determined the surface brightness of individual stars usingour model, and checked that it is consistent with a recent surface brightness-- color relation. We compared our results with evolution theory models ofmassive stars and found they agree in general, however, models with higherovershooting values give more consistent results. The age of the system wasestimated to from 11.7 to 13.8 Myr, depending on the model.

Towards early-type eclipsing binaries as extragalactic milestones: I. Physical parameters of OGLE-LMC-ECL-22270 and OGLE-LMC-ECL-06782