The Italian manager was taken back by Magpies boss Rafael Benitez's decision to go with five at the back, as his side maintained their 100% start to life in the Premier League.
In an interview with Sky Sports after the game, Sarri spoke of his surprise at how Benitez had set his team out for the game.
"I was surprised at Rafa. In Italy, I have never seen him play with five defenders so I was really surprised. The match was very difficult, they were so low and compact, it was impossible to have spaces.
"We got better in the second half but it was a very difficult game. I think we showed improvement because the match was difficult it was not easy to play well."
Sarri continued by admitting that he had been impressed by Eden Hazard's performance, though in an ideal world, he would have been able to replace his Belgian superstar before the end of the game.
"Eden has played very well. Maybe it was better it he played for 75 or 80 minutes, but (Mateo) Kovacic asked for the sub so it was impossible [to take him off]."
The Blues victory was their first at St James' Park since 2011, with Hazard's penalty, and a late DeAndre Yedlin own goal helping Sarri's side earn their third consecutive Premier League victory.