This paper demonstrates a rapid and full hitless defragmentation method in elastic optical networks exploiting a new technique for fast wavelength tracking in coherent receivers. This technique can be applied to a single-carrier connection or each of the subcarriers forming a super-channel. A proof-of-concept demonstration shows hitless defragmentation of a 10 Gb/s QPSK single-carrier connection from 1547.75 nm to 1550.1 nm in less than 1 µs. This was obtained using a small (0.625 kB) link-layer transmitter buffer without the need for any additional transponder. We also demonstrated that the proposed defragmentation technique is capable of hopping over an existing connection, i.e. 10 Gb/s OOK at 1548.5 nm, without causing any degradation of its real-time Bit Error Rate (BER) value. The proposed scheme gives advantages in terms of overall network blocking probability reduction up to a factor of 40.