The Big Georgian Dawg has only one slight chance to defeat Roger..He has to keep his first service percentage close to 70 % and cannot double fault more than 3 Times.. The best coaching advice John can receive can come from his wife.."To be a great lover, You don't have to be a porn star but be able to hit all the right spot at the right time, " That's what makes John's service so lethal is next to Fed, he is probably the best as service placement. Just serve to a spot and don't focus on what Roger's return of service positioning should be what his coaching advice should be.
If Roger isn't playing like TMF or as Darth has reference him at times ATP Fed, Isners lack of mobility will still get exposed by Roger's brilliant off pace slice backhand which he did so Excellently vs Anderson. otherwise
So it's up to John , if he chooses to serve like a porn star ..Fed in a close 2sets otherwise if he served like a great lover this can go 3 set, however the odds still favor Roger.