Inter Milan bounced back to winning ways and extended their lead at the top of Serie A to 21 points after a clinical 5-0 win at relegation battlers Frosinone.Davide Frattesi gave Inter an interval lead before Marko Arnautovic struck a decisive second against the run of play.Inter substitutes Tajon Buchanan and Lautaro Martinez scored within the space of three minutes in the closing stages and Marcus Thuram added a late fifth.twitter:1789032642983129189Simone Inzaghi’s side, crowned Serie A champions at the end of last month, were not at their best, but were brutally clinical with all five of their efforts on target resulting in goals.Inter slipped to a shock 1-0 defeat at second-bottom Sassuolo last week – their second league loss of the season – and Frosinone twice threatened to take an early lead.Luca Mazzitelli’s shot from outside the box flashed narrowly wide and Inter goalkeeper Yann Sommer fumbled Matias Soule’s long-range effort before gathering the spinning ball at the second attempt.But the home side’s good work was undone when they lost possession in their own half in the 19th minute. Thuram darted into the box and his low cross was bundled in off Frattesi’s thigh after deflecting off a covering defender.Frosinone twice went close to equalising before half-time as Marco Brescianini’s thumping drive was brilliantly saved by Sommer at full stretch before Walid Cheddira’s shot crashed back off the crossbar.The home side also had Inter on the back foot at the start of the second half with Reinier and Cheddira forcing Sommer into further saves and Emanuele Valeri shooting wide.Inter were made to look shaky at the back, but they scored the crucial second goal on the hour-mark.Frattesi was this time the provider, running on to Nicolo Barella’s clever through-ball and crossing low for former Stoke and West Ham forward Arnautovic to side-foot home his first goal since February.twitter:1789032873816699122Stefano Sensi teed up Buchanan to fire home an angled shot for Inter’s third in the 77th minute and three minutes later Martinez despatched a left-footed finish into the bottom corner.Thuram completed the scoring in the 84th minute, racing clear from halfway and lofting a neat finish over Frosinone goalkeeper Michele Cerofolini.Frosinone remain two points clear of the drop zone, but relegation rivals Udinese and Sassuolo both have a game in hand.