  We present a study of the properties of the O-type, massive eclipsing binary
2MASS J13130841-6239275 located in the outskirts of the Danks 2 cluster in the
G305 star-forming complex, using near-infrared spectroscopy from VLT/ISAAC. We
derive the masses and radii to be 24.5$\pm$0.9 M$_{\odot}$ and 9.2$\pm$0.1
R$_{\odot}$ for the primary and 21.7$\pm$0.8 M$_{\odot}$ and 8.7$\pm$0.1
R$_{\odot}$ for the secondary component. In addition, we evaluate the
sensitivity of our parameters to the choice of the spectral features used to
determine the radial velocities. Both components appear to be main-sequence
O6.5$-$O7 type stars at an age of $\sim$5 Myr, which is in agreement with the
age of the cluster. A high visual extinction of A$_{5495}$=11.9$\pm$0.1 mag is
reported, which is likely attributed to the cold molecular gas contaminating
the north-east region of the cluster. By fitting the spectral energy
distribution of the system to the available $BVI_{c}JHK_{s}$ photometry, we
determine a distance to the system of 3.52$\pm$0.08 kpc with a precision of
2$\%$, which is the most well-determined distance to the Danks 2 cluster and
the host complex reported in the literature.
