A Quick Puzzle from the London Chess Classic

Hi Chess Friends,

I was watching the London Chess Classic coverage today, as Anish Giri was finishing off Hikaru Nakamura and Alexander Grischuk and Levon Aronian were analyzing after their draw. Those two Super GMs and the commentators were analyzing Giri's game and wondered why Black played Rg5 instead of Bc7 (aiming for a fortress) in the position below.

Grischuk very quickly pointed out a strong variation, where black would be knocked out after Bc7. Very few people out of the world's elite could find the moves in seconds like he did, but see if you can find the win at your own pace.