you never get a rematch per credit. You can get a rematch by adding a credit after your defeated the first time- and as far as i know, thats how TG is set up.
My high score is 204810. Doubt i could do it again, though. I managed about 175k tonight. Its all about patterns. The first round each opponent has a knockout pattern that once you learn it is obvious. I never took a hit until bald bull, and he landed one. After that, i didn't take another hit until Sandman. He's by far the toughest of the bunch. Beat him on the first round though. Ended up getting my butt kicked by glass joe, and then beating him in the rematch only to get killed by Piston Hurricane. I still haven't worked out the second round patterns yet. Glass Joe is super tough to hit on the second round. Seems you just about have to hit him just before he tries to throw a punch. PH second round you just have to dodge left and hit him while he's all stretched out. Anyway, point is, where you can almost throw punches at will in the first round, its not that way in the second round. You've really got to plan your punches well, and know the limits on combos. Trying to throw an extra punch will get you knocked down in the second round, unlike the first.