Grimus clocked 53.88 seconds, just nine one hundredth of a second behind pace setter Finland's Jouni Pellinen in the World Cup season opener at the Innichen/San Candido resort.
Despite his strong showing in qualifying, the AIS athlete was beaten in his first elimination final, finishing the day in 17th place in the field of 67.
In other Australian ski cross results Scott Kneller finished 19th and in the women's event Olympian Jenny Owens placed 17th, Sami Kennedy, 19th and Katya Crema in 23rd position.
Australia's five-person ski cross team compete again tonight in the second round double header.