The Argentinian went one better than great rival Cristiano Ronaldo's hat-trick earlier in the evening as he was part of a Barca side who utterly outclassed woefully inferior opposition.
His second was his 200th goal in the Primera Division, another landmark feat in his ever-growing list of achievements.
The fourth brought his total in the league this term to 33 and he is on track to match last season's barely-believable 50. Seventeen more are needed from 17 games; only for Messi would that be considered simple.
And next up for him, albeit in the Copa Del Rey semi-finals: Real Madrid at the Bernabeu on Wednesday.
Pedro was also on target for the Catalans, while Raoul Loe briefly levelled for Osasuna before Alejandro Arribas' sending-off after 27 minutes made their task an almost impossible one.