This comes from one of my recent games. I haven't checked this with an engine, so please let me know if there are any improvements for either side. Note that (although I believe it makes no difference) in the actual game, a Scotch Game, Steinitz variation, Black has twice moved his King, so he cannot castle.

What if 18. ... Qa5?

After 18...Qa5 I guess White still wins after 19.Qd7+ Kf8 20.Qxd8+ Qxd8 21.Rxd8+ followed by RxR.

Yes but my point was that its not a mate in 6. That line would have several more moves to mate

Thanks for the feedback, crimsonaaron. I don't know how I missed 18...Qa5. (Probably the same way I missed a mate in two earlier in the same game.) So perhaps I should have presented it as a mate in 5 starting one move later. My opponent in the game played neither ...Qa5 nor ...Nc6, after my 18.Rd1, opting instead for the less torturous ...1-0.

Also I personally like 22. Rd8+ for the matw just to make them give up their queen before they lose with 22. ...Qe8 23. Rxe8# (23. Qxe8#)