The Nerazzurri had been unbeaten in the league in 2017-18 before losing 3-1 at home to Udinese last week.
Rather than shrug off that result, they were undone by Diego Falcinelli's goal to go down 1-0 at Sassuolo this weekend, allowing Napoli to extend their advantage at the top of the table to five points.
Spalletti, though, is adamant his team has no cause for concern as they approach the second half of the campaign.
"I am even more convinced than ever that Inter know what they're doing, because I saw the right performances in both these games," he told Mediaset Premium.
"There are moments when we're not so consistent or lack a bit of smarts, such as conceding an avoidable goal on the counter-attack.
"We should've done better in that situation and we didn't make the most of our own scoring opportunities, which is why this defeat happened.
"We had chances that went close to the upright or others where we weren't sharp enough.
"The team put in the performance, it was aggressive and constantly pushed Sassuolo back into their own penalty area. We could've done with a few more quality passes.
"We paid a heavy price for mistakes in key moments.
"I saw a reaction when we went behind and we put so many balls into the box."