Hi, so heres my guide to getting this achievement.
First off I'm not going to say "all you have to do is" or "it's simply a case of" or "you can easily", this achievement has a high ratio for a reason, it's challenging. You will need patience, luck and skill to get it, unless of course you are some sort of gaming God, I'm not so I needed all the above.
You will probably find that there are only 2 characters that give you a problem each time you play-through, Jung Soo and Mark, so this is really a combination of methods that worked for me when beating them myself,
Most people know that you can adjust the game parameters for the tournaments in the game options menu, so set the games to 1 of 1, points per game = 7 and points per serve = 5. (if you haven't got The All-Star yet (my advice use Mark), you can restore default settings).
I've found that you can get an ace serve past everyone except Jung Soo and Mark.
Some people have asked me to say where to stand for each one, but this isn't practical, there are several spots to stand in to get an ace, and although you can often use the same spot, you may need to alter it depending on who you are playing with or against.
For example, you could stand 6 sidesteps right and one back, then use X holding down and left and get an ace, then against the next opponent they will return that type, but by standing 7 sidesteps and using X holding left you will ace them.
Ace positions that worked for me included
1. 4 sidesteps to max sidesteps right, X and hold left
2. 4 sidesteps to max sidesteps right and back one full (or the little shuffle), X and hold left
3. as 2, but hold down and left
Try to get max power and spin if you can.
The most common position seemed to be 6 or 7 sidesteps right, 1 back, X holding down and left, althought 7 sidesteps right, X holding left also worked well.
As it differs with who you play as and against, use the above as a basis and you shouldn't go far wrong, don't expect to get ace serves everytime against every player, but I found if they returned my first shot I needed to change my ace serving position and that usually did the trick.
Jung Soo and Mark. (sometimes Juergen)
Dont try to ace serve them, they will return it everytime, try using a low powered Y, aimed to the left generally, I found that if I served with the speed bar at around 30ish % (usually at the level the outer edge white spin meter gets to) they didn't do an unreturnable return of serve.
I did find that Carmen was able to do a B based Ace serve (sidestep left) attempt that forced Jung Soo so wide when he returned I was able to immediately counter and win a point everytime.
This doesn't work everytime, but by returning with a Y&B and holding down and right, quite often they will return it into the net, or it will drop over the table and they can't return, it works better against some than others, but it is a cheap way to get points and is usually a safe way to keep the ball in play.
This is vital when playing against Jung Soo and Mark, but helps with some others. Each player has a side where they can return very fast low shots, hard to counter, so try to keep them on the opposite side, I prefered to keep playing to Jung Soos right and Marks left (but Mark is tricky so I varied it depending on who I was playing as).
It's boring but try to use LB&Y holding down and left, hitting across the table onto their right. This keeps the play sort of slow and you can win points by either them playing it into the net, or under the table, or with time you will get an opportunity to do a X or X&A and force them very wide, you can then counter with a A or B&A to the opposite side. This does not work every time, but more times than not, and can be flipped so you play onto their left and use B or B&A to send them wide, countering with A, X, or X&A.
Some characters build up the bar quickly, which is helpful, so use it when you have it, but don't worry about trying to fill it, let it happen and just concentrate on staying in the rally. I found that using with the focus using a Y&B onto their left gave a good opportunity for a counetr X&A to their right.
This game will frustrate you, so I broke it down. I would play through until I got to Jung Soo, give it a few goes and if i kept losing, turn it off and play something else, then come back to it and find I beat him fairly quickly, I did the same with Mark, the good thing is once you beat Mark the match for the final is usually easy as they will be vunerable to ace serves.
With some characters I actually found it easier to win points from their serves than my own, so if you are struggling you can try that approach.
Well, thats about as much information as I can pass on, I wish you well and good luck in your attempts to beat that git Mark.