Watson has endured a dismal series that saw him lampooned for repeatedly getting out lbw, but the all-rounder at least partially redeemed himself as he put England debutants Chris Woakes and Simon Kerrigan to the sword in south London.
With the Ashes already retained, England made the surprise decision to experiment with their line-up, bringing in Warwickshire all-rounder Woakes for Jonny Bairstow and Lancashire left-arm spinner Kerrigan for the injured Tim Bresnan.
It had been widely anticipated Surrey pace bowler Chris Tremlett would return on his home ground after impressing in the 2010-11 Ashes in Australia.
Asked if he was shocked to see England’s changes, Watson said: “Yeah I was actually. I was expecting Tremlett to play to be honest. He had quite a lot of success against us in the last series in Australia.
He bowled beautifully in the Tests he played. I was certainly a bit happier to face Woakes and Kerrigan than a guy (Tremlett) who is 6ft 8in and sends balls bouncing around your face. I’m certainly not complaining.
“You could definitely sense he (Kerrigan) was very nervous in those first couple of overs. There’s no doubt it’s extremely nerve-wracking, especially if someone tries to get after you in your first Ashes Test.
“You are pretty much exposed out there and you have to try to find a way through it. He will certainly learn from it.”
The 32-year-old’s third Test hundred was his first in 25 matches and 48 innings since his previous best of 126 against India in October 2010.
And Watson, playing his 46th Test, revealed he had been through an emotional time while trying to battle his way out of the slump. “I have had a lot of soul-searching over this last month, more than at any time in my career,” he said.