It worked for me so it should work for you. I have latias and latios so I'm going to tell you how to catch them easily without a master ball. I caught both of them with a timer ball. What you do is get a wobbufet at level 31-35 and you will need alot of potions like max potion and hyper potion so your wobbufet doesn't die. Wobbufet has the ability for your opponent not to flee. Put it in first and when you encounter latias or latios, use mirror coat only once. It will bring it down to either yellow or red. After that don't attack her at all cause you know if you kill latias you won't be able to find her. There's only one in the whole game. But for in case if you are in the same area as she is, save it so if you do kill her just turn it off and back on and she will still be in the game. So as I was saying use mirror coat once and after that just keep on throwing timer balls at her but also use potions for wobbufet so he will stay alive. Keep on throwing timer balls and after a couple of turns you'll have latias.
P.S. Buy at least more than 50 timer balls