Argentina attacker Martinez netted a first-half header from a Dalbert cross to set Inter on their way to a fifth win in their last six games in all competitions.
Inter, who named stars including Mauro Icardi, Ivan Perisic and Marcelo Brozovic on the bench, spent much of Saturday’s San Siro clash on the back foot but Politano’s late goal made sure of the points.
Cagliari, now winless in four Serie A games, could not find a way to break down Luciano Spalletti’s resurgent side with Daniele Dessena’s second-half strike rightly ruled out for handball.
With Icardi on the bench, Martinez started up front and he made an early impact with the opening goal in the 12th minute, heading in a left-wing Dalbert cross.
Samir Handanovic captained Inter in Icardi’s absence and the goalkeeper bravely dived at the feet of Leonardo Pavoletti as the striker tried to turn in a Paolo Farago cross, taking a knock to the head but continuing after receiving treatment.
Antonio Candreva had a great chance to make sure of the points in the 62nd minute when he was sent through into the box by Politano, but the Inter winger fired straight at Alessio Cragno.
Cagliari’s goalkeeper made another strong save to push away Politano’s long-range drive and the visitors seemingly levelled in the 72nd minute.
But replays showed Dessena finished with his arm as he bundled a cross over the line, with Inter grateful for VAR again following the chaos at the end of last weekend’s 1-0 win at Sampdoria.
And Inter wrapped up their third straight Serie A win in the 89th minute when Politano let fly with a sensational volley from just inside the box, a small deflection giving goalkeeper Cragno no chance.
What does it mean: Spalletti’s side back on track
Inter started the season badly but the Nerazzurri are on an upward curve after a strong run of results. That they secured this win without some of their most important players, who were rested for the Champions League, was all the more impressive.
Martinez proves credentials
Leaving Icardi out is always going to make headlines but Martinez showed he is an able deputy for his fellow Argentina attacker. Martinez looked sharp from the off and although Cragno perhaps should have saved his winning header, the power behind the effort was impressive.
Wasteful Candreva lucky
With Perisic on the bench, Candreva was under pressure to deliver for his side but he was fortunate a poor effort in the second half did not cost Inter. Candreva should have buried a clear chance but lacked composure and shot at Cragno’s legs.