The Argentine looked sharp from the off on Tuesday, inspiring Inter from the front as Luciano Spalletti's side made light work of the Sardinians.
Having twice gone close to netting in the first half, Icardi got the goal his performance deserved four minutes after the interval - moving him onto 25 for the league campaign, his best ever tally.
Joao Cancelo's first Serie A goal had put the hosts ahead early on, with only wasteful finishing from youngster Yann Karamoh and excellent goalkeeping from Alessio Cragno denying Inter a second before the break.
Icardi's goal opened the floodgates, though, with Marcelo Brozovic curling in a delightful third on the hour before Ivan Perisic put the result beyond all doubt in stoppage time.
Spalletti's side now sit, temporarily at least, two points ahead of Lazio and Roma, with the race for the final Champions League places looking set to go down to the wire.
Inter wasted no time in halting their three-game goal drought, Cancelo putting them ahead inside three minutes when his inswinging free-kick somehow drifted through a crowd of players and into the far corner.
Cagliari were fortunate not to be two down five minutes later - Cragno doing well to keep out Perisic's effort before Karamoh shot wide after getting one-on-one.
Karamoh looked set to atone for that miss moments later, only for the winger to volley against the bar following fantastic play from Icardi, before Cragno pulled off another fine save to deny Rafinha a maiden Serie A goal.
Cagliari had Leandro Castan to thank soon after, as the former Roma defender got across to deny Icardi from point-blank range.
Karamoh finally put the ball in the back of the net in the 45th minute, only for the goal to be disallowed for offside, with Icardi again going close in stoppage time.
Inter's captain did not have to wait long for a goal following the restart, however, keeping his cool to prod home from close range after getting the better of his marker with some neat skill.
Cagliari's luck was out, and Inter soon made it three - Brozovic giving Cragno no chance with a sublime finish into the right-hand corner.
Cancelo was the next to try his luck as Inter pressed for a fourth, the full-back finding the roof of the net with a dipping long-range effort, while Karamoh saw a powerful effort well-saved by Cragno.
VAR was called upon late on when Marco Andreolli appeared to handle Antonio Candreva’s goal-bound shot, but the referee decided against awarding a penalty.
Ultimately those misses mattered little as Perisic wrapped up a comfortable win with a crisp strike from 20 yards, Inter warming up nicely for a run-in that includes clashes with Juventus and Lazio.
