After four minutes, Leicester took the lead thanks to a superb goal from James Maddison.
The Foxes playmaker drew away from Thiago Silva and blasted a shot past Edouard Mendy.
Alonso equalized by volleying in a cross from Reece James.
Lukaku himself squandered a good chance by heading Hakim Ziyech’s cross beyond.
Chelsea: Mendy, Chalobah, Silva, Rudiger, James, Jorginho, Kante (Loftus-Cheek 72), Alonso, Ziyech, Pulisic (Azpilicueta 72), Lukaku, Alonso, Ziyech, Pulisic (Azpilicueta 72), (Havertz 82).
Kepa, Saul, Barkley, Mount, Kenedy, and Sarr were not used as substitutes.