What was the correct defence here?

Okay guys so I just finished playing a 10minute blitz and my opponent offered up a knight sac which surely must have been unsound. I spent the rest of the match trying to piece together some form of defence but time was getting the better of me and I lost the match with 33seconds left on my clock whilst my opponent had considerably longer.

Dear,  

    what was wrong with 21.Rf1

It puts the pressure on the f7pawn ,may be somethinglike h4 to put your black square Bishop into the attack .... Black has to defend now and then you can collect yourself, coordinate your pieces and go on from there.

Black had a big material loss to go for any kind of endgame, so he did the right thing; Attack.... simply, he was losing and could not lose more. 

You should have stop this attack by your counter attack, as long as the game was really open, and your King had no true pieceful square.

At least this is how I see it.

27. Ra4 (if 27... Rxa4 then 28. Qxa4 Qxe5+ 29. Kf1 Rc4 30. Qa3 Qf4 etc.) Qxe5+ 28. Kf1 Rh8, 29. Kg2 etc.

Black's knight sacrificial offering helped open up the a,b,c columns and allow his rook to come down.  Instead of taking the knight, you may have considered to put pressure on his queen and take control of column a:  13. Rb1 (if 13 ... Qa3 then 14. bxc6 Bxc6 15. Bxc6+) [if 13... Qc4, then just trade queens because the Black queen has great positioning and the white queen does not] Qa3 14. Rb2 Nxa4 15. Ra2!

I think 6.Kb3 is a mistake.It moves the king on the queenside where the battle is going to take place

21. Rf1 certainly looks like the move to me. If I wanted to get my rook onto the f file why did I go about it in such a long way? Maybe it was time pressure or I simply thought it would be necessary to add an extra defender to my bishop on a4.

Oh, and black wasn't down material before the sac either. In fact, he was the exchange up.

Here's the full-length match. In hindsight I played dreadfully here, so many mistakes were made and I could have even avoided the exchange. Maybe his gimmicky opening system was the cause of my reckless and inaccurate play.