The South Tyneside club are aiming to reach the fifth-tier of English football for the first time in their history, but lost their one-point lead at the top in the penultimate game of the season last Saturday to fall two points behind.
They needed a 95th minute equaliser to scramble a point at home to Bedford Town, while Fylde coasted to a 4-0 success over Southport.
Their goal difference is now two better than South Shields and have scored nine more goals, so if they draw at Merthyr, the Mariners would need a three-goal margin of victory to achieve automatic promotion.
“You spin your head thinking about all the other outcomes,” said Watson. “Ultimately, that is just stuff I can’t control.
“All I can control is the energy we bring into training and making sure we’re totally ready for Saturday.”
If unsuccessful, Shields would drop into the six-team play-offs including the likes of FA Cup giantkillers Macclesfield with only one team being able to win promotion.
“There are a lot of variables, but the most important is we’ve just got to do our job,” said top scorer Paul Blackett.
“Win the game and if it doesn’t [go our way], we go into the play-offs next week obviously full of confidence as well.”
