Veteran Kevin Phillips scored a brace as Blackpool came from two goals down to draw 2-2 at Brighton.
Barnes first crossed from the left for Mackail-Smith to head home before slotting from close range after a goalmouth scramble.
Phillips, 38, followed up his 60th minute header by levelling in stoppage time.
The ball fell to the striker who turned and volleyed in to the bottom right hand corner.
Brighton remain unbeaten for the season and lie third in the Championship on 10 points, while Blackpool are a further three points back in seventh.