I always keep a bottle of club soda under my sink for just such emergencies. It is acts like Oxyclean but is in liquid form. Then I do the washing. Unfortunately I do find tomato one of the hardest stains to get out.

I put the stain over a glass or bowl, depending on it's size, and keep pouring the club soda through it until the stain disappears. The product called OXYCLEAN is excellent as well and I also keep it under my sink. I have found that the relatively new spray bottle of pretreat oxclean doesn't work as well as mixing up the powder and using it while is still bubbles.
Good luck - I hope you get the stain out. I am just sick when something I love seems to be ruined.