I want to try and give you some advice on what I would do. Its hard to explain so I will try.
#1 Rather than brush into the background of the center pic what I would do is take advantage of the fact that the Overeem pic on the left makes a natural border. I would trim everything on the right of Overeem from the left pic and use the background from the center pic to fill the void that I have circled. If needed the clone stamp tool sometimes works to extend certain backgrounds like the white of the mat. May take some practice to make it work but it will be worth it.
#2 Same thing here Overeem and his opponent make a natural border use it as a cut off point.
If you don't understand what I mean email me and you can Email me the PSD file and I will do it to show you what I mean.