  The ESPRESSO spectrograph is a new powerful tool to detect and characterize
extrasolar planets. Its design allows unprecedented radial velocity precision
(down to a few tens of cm/s) and long-term thermo-mechanical stability. We
present the first standalone detection of an extrasolar planet by blind radial
velocity search using ESPRESSO and aim at showing the power of the instrument
in characterizing planetary signals at different periodicities in long time
spans. We use 41 ESPRESSO measurements of HD\,22496 within a time span of 895
days with a median photon noise of 18 cm/s. A radial velocity analysis is
performed to test the presence of planets in the system and to account for the
stellar activity of this K5-K7 main sequence star. For benchmarking and
comparison, we attempt the detection with 43 archive HARPS measurements and
compare the results yielded by the two datasets. We also use four TESS sectors
to search for transits. We find radial velocity variations compatible with a
close-in planet with an orbital period of $P=5.09071\pm0.00026$ days when
simultaneously accounting for the effects of stellar activity at longer time
scales ($P_{\rm rot}=34.99^{+0.58}_{-0.53}$ days). We characterize the physical
and orbital properties of the planet and find a minimum mass of
$5.57^{+0.73}_{-0.68}$ $\mathrm{M}_{\oplus}$, right in the dichotomic regime
between rocky and gaseous planets. Although not transiting according to TESS
data, if aligned with the stellar spin axis, the absolute mass of the planet
must be below 16 $\mathrm{M}_{\oplus}$. We find no significant evidence for
additional signals with semi-amplitudes above 56 cm/s at 95% confidence. With a
modest set of radial velocity measurements, ESPRESSO is capable of detecting
and characterizing low-mass planets and constrain the presence of planets in
the habitable zone of K-dwarfs down to the rocky-mass regime.
