We report the detection of neutral deuterium in the low-metallicity damped Lyman-alpha system at z(abs) = 2.621 towards the quasar CTQ247. Using a high signal-to-noise and high spectral resolution (R = 60 000) spectrum from the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph, we precisely measure the deuterium-to-oxygen ratio log N(D-I)/N(O-I) = 0.74 +/- 0.04, as well as the overall oxygen abundance, log N(O-I)/N(H-I) = -5.30 +/- 0.10 (or equivalently [O/H] = -1.99 +/- 0.10 with respect to the solar value). Assuming uniform metallicity throughout the system, our measurement translates into (D/H) = (2.8(-0.6)(+ 0.8)) -0.6) x 10(-5). This ratio is consistent within errors (<0.4 sigma) with the primordial ratio, (D/H) p = (2.59 +/- 0.15) x 10(-5), predicted by standard Big-Bang nucleosynthesis using the WMAP7 value of the cosmological density of baryons (100 Omega(b)h(2) = 2.249 +/- 0.056). The Di absorption lines are observed to be broader than the O-I absorption lines. From a consistent fit of the profiles we derive the turbulent broadening to be 5.2 kms(-1) and the temperature of the gas to be T = 8800 +/- 1500 K, corresponding to a warm neutral medium.