His Aston Martin team knew in advance that Monza wouldn't play to the strengths of the AMR23, and that was reflected in qualifying, with Alonso earning 10th place and his lowest grid position of the season.
Despite a typically feisty race, the Spaniard could not better ninth in the race, which matched Hungary as his worst result of the year, but at least extended his record of scoring in every event thus far.
"Obviously many, many lessons we need to take from this race," he said. "We were not competitive, so that's the main focus for us, to try to understand in this type of circuit what we need to do differently into the future, also next year when we come here.
"Race-wise there is not much to talk about, we were slow from the beginning to the end, and it was not possible to fight better than ninth.
"So we take these points, but hopefully many lessons."
Asked if it was frustrating not to have a competitive car, he said: "It is frustrating because it was a very demanding race mentally and physically to drive the car that was, with very low grip, very tricky to drive. So for me one of the most difficult races of the year.
"And it's the worst result, so it's going to be an anonymous race and no one will remember this. But I will do it in my head, because it has been a tough one.
"But as I said, hopefully good lessons that we take from here on the car or the data that we have from the race, and we get better next time."
Expanding on what went wrong, he added: "I think the car and the efficiency of the car maybe is not as good as it should be in this type of track where the drag level is very important, and it seems that has been our weakness. We know that. Now we need to get better, and bring some ideas."
Alonso admitted he was pleased to have at least got the most out of the package he had in Italy.
"I think we are doing the job every Sunday," he said. "Executing the maximum from the car, sometimes unfortunately it's ninth like today, sometimes it's second like last week [at Zandvoort].
"We are not doing mistakes. We are doing good strategy, good pit stops, not making big mistakes like some of our competitors, [like] they made at the beginning of the year. So we have a good gap in terms of points.
"But yeah, it's getting closer, and even Ferrari in the constructors' championship, I think, is ahead of us now with this result. Let's try to bounce back in Singapore."