Helped by a disastrous performance from Sassuolo defender Vlad Chiriches, Inter were unrecognisable from the team that lost 2-0 at home to Real Madrid in the Champions League on Wednesday as they dominated the match from start to finish.
The win, capped by an exquisitely-taken Roberto Gagliardini goal in the second half, moved Inter into second place with 18 points, ahead of Sassuolo on goal difference and two behind leaders AC Milan.
On a wet, miserable afternoon, Inter, who rested striker Romelu Lukaku, needed a confidence booster after Wednesday's sorry display and were given it with some help from Chiriches in the fourth minute.
Inter were firing on all cylinders and 10 minutes later, Arturo Vidal's cross ricocheted off the hapless Chiriches and into the net for the Milan side's second goal.
Chiriches's unhappy afternoon ended when he limped off with a muscle injury three minutes before the break.
Sassuolo struggled to find their usual fluid style although Filip Djuricic curled a shot against the post before half-time.
The hosts improved after the break but, vulnerable on the counter, they were caught out on the hour.
Inter, who are Serie A's leading scorers with 23 goals, won possession in midfielder and Matteo Darmian's pass found Gagliardini who flicked up a bouncing ball with his left foot and volleyed into the far corner with his right.