At stumps on today's first day, Australia were 307 for four as they sought a consolation victory in a five-match series already won by England at 3-0 up.
Watson put a disappointing series with the bat behind him with just his third Test hundred -- his first in 25 matches and 48 innings since his previous best of 126 against India at Mohali in October 2010.
The 32-year-old all-rounder, playing his 46th Test, was especially severe on debutants Chris Woakes (none for 52 in 15 overs) and left-arm spinner Simon Kerrigan (none for 53 in eight), chosen after England opted against recalling fast bowler Chris Tremlett on his Surrey home ground.
"Getting hit on the head helped me because it took my mind off getting through the nineties.
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"I faced Simon Kerrigan in the tour match at Northampton (against the second-string England Lions) last week and I knew what to expect."
Watson, filling Australia's problem position of number three after starting the series as an opener and then moving to number six, received good support from Steven Smith (66 not out) in an a fourth-wicket stand of 145.
Michael Clarke, trying to avoid becoming the first Australia captain to lose a Test series in England 4-0, unsurprisingly chose to bat first after winning the toss on a good pitch.
However, England had an early breakthrough when David Warner played a loose shot outside off-stump to James Anderson and was caught behind for six.
But with England's bowlers failing to gain much movement, Watson, hitting through the line with confidence, was 80 not out at lunch.
Chris Rogers, who helped Watson add 107, then fell for 23 when he edged off-spinner Graeme Swann to Jonathan Trott at slip.