The Hawks trailed by one point heading into the final quarter in Launceston on Saturday against an opposition needing a victory to boost their AFL finals hopes.
But they did enough to hold on for the 14.15 (99) to 12.11 (83) result, with Mabior Chol getting a crucial breathing-space goal at the back end of the game.
With his side ahead by 11 and less than six minutes on the clock, Chol earned a free kick with a tackle and then nailed a goal from about 50m out near the boundary line.
North cut the margin to 10 points with less than three minutes left thanks to Harry Sheezel but were left to rue several key misses in the fourth quarter.
Watson's haul gives him 52 goals for the season, putting him right in the hunt for the Coleman Medal.
"Every week he gets a fair bit of attention and for a player so young he works his way through it really well," Hawthorn coach Sam Mitchell said.
"It's very difficult to be consistent. He was really important."
Jai Newcombe was also heavily involved for the Hawks and picked up a game-high 34 disposals, plus 12 clearances and one goal assist.
Hawthorn, who are in third spot and just two points behind Sydney, have won four in a row ahead of a blockbuster against reigning premiers Brisbane on Friday.
The Kangaroos have slumped to five losses on the trot and sit 13th on the ladder.
"Finn O'Sullivan at the 20 minute mark of the last quarter, snaps, should be a goal," North Melbourne coach Alastair Clarkson said.
"Jack Darling takes a mark 30m out last quarter, should be a goal.
"We're competing and we're getting closer to some of those sides but it also tells us that we've got a way to go.
"At AFL level those shots and opportunities should be executed."
Hawthorn nabbed the opening goal of the game through Will Day before the Kangaroos got four straight for a 26-9 lead at the first break.
North Melbourne's Nick Larkey, who has struggled for accuracy in recent times, produced a shocking first shot but nailed his second from off centre.
Team mate Zac Banch squeezed one through from the goal square in the last minute of the first quarter to give his side a boost.
Hawthorn came to life early in the second with Watson, who only picked up one touch in the first term, getting three goals in a row including two in 60 seconds.
The lead then changed hands multiple times before a behind after the halftime buzzer to Chol levelled the scores at 46-46.
Watson fired again with two goals early in the third before a major to Chol broke the run of tit-for-tat scores as Hawthorn threatened to pull away.
But the Kangaroos rallied and Larkey's second gave his side a 69-68 lead heading into the final quarter.
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