Thomas Frank wished for a little Christmas miracle and Brentford are unlikely to have a better chance of taking down the European champions but this night will go down as a triumph for Thomas Tuchel.
The Chelsea boss juggled his squad, started with three teenagers, resisted early pressure and relied upon goalkeeper Kepa Arrizabalaga to make crucial saves in the first half, before releasing his stars from the bench to force the win.
The goals came courtesy of an 80th-minute own goal fired into the top corner by Pontus Jansson as he tried to intercept a fierce low cross from Reece James.