Lukaku joined Inter in a club-record deal after leaving Premier League giants Manchester United last month.
The 26-year-old has already scored two goals in two games for Antonio Conte's Inter, who are looking to dethrone Italian champions Juventus this term.
Sanchez followed Lukaku to Inter from United on loan and the Chilean heaped praise on his star team-mate.
"You won't find anyone else like him, anywhere in the world," Sanchez told ESPN FC .
The pair had their struggles at Manchester United, with Lukaku claiming he was a scapegoat for the club , but Sanchez doesn’t think they were given a real chance to show their best.
"Lukaku and I trained very well. But we needed to play more in games to get to our best.
"It wasn't the right time for us to be at Manchester. Too many changes. When you change that much, it's tough.
"Lukaku and I trained very well.”
The move to Inter has opened up a new set of chances for both players.
Inter finished fourth in Serie A last season, but a rebuild of the squad over the summer has Conte’s men looking like real challengers to Juve’s crown, and the Chilean claims that’s why he and the Belgian star both made the move to Milan.
“I can feel the will here to achieve. This is why I'm here,” he said.
"That's why Romelu is here. Will it work? We will have a lot more to say about that at the end of the season."
Lukaku scored 42 goals for United across all competitions following his move to Old Trafford from Everton in 2017.
Sanchez swapped Arsenal for United in a high-profile transfer in January last year, however, form and injuries limited the 30-year-old to just five goals.
Inter host Udinese on Saturday, with Sanchez looking to make his debut for the Nerazzurri as they look to keep up their perfect start to the new season and hold onto their place at the top of the table.