Sorry for my English.
When I want to defend a lead and the opponent switch to 4-2-4 I switch to deep defensive line, and turn on the "tight marking" mode. Left winger mark opposition Right winger (But not tight marking) to help the left full back. The winger closing down whole pitch so when the opponent's full back will join the attack he will tackle him. Same thing on the other side.
About the middle- Playing with 2 MC and one DM. The two MC Mark tight the opponent MC, they closing down almost only in own area and the DM closing down almost whole pitch so he can help them.
Also I turn on the counter attack mode, playing down both flanks, slow tempo, direct passing, wide game, and not much but many time wasting.
Also remember that that full backs should not make forward runs.
I am managing Fiorentina, I played against chelsea in CL and i grabbed a goal. In the 75 or 80 minute Chelsea played with 4-2-4 and it worked well.