I think I remember that struggle. Our Walmarts offer 2 options, one like a 12 oz Great Value and another similar size non store-brand.
Soak just the cap in a saucer of hot water for 3 or 4 minutes (i.e. turn the bottle upside down and balance it in a saucer or dish with an inch of hot water). That will cause the cap to expand a micron. Then use a pipe-wrench to unscrew the top.
