The five-times champion finished his British Open campaign with a real flourish, recovering in style from a first-hole bogey to squeeze five birdies in a four-under-par 68 and earn a highly creditable total of 289, one over par.
Watson hardly missed a fairway all day as he outshot 43-year-old U.S. PGA Tour regular Senden (71) by three strokes.
"It was a fun day today," the veteran American told reporters under blue skies and bright sunshine at Royal Liverpool.
"I put the ball in play off the tee. On the first day I missed six fairways but I'm not sure I missed one today.
"I think the golf course is there for the taking. The par-five 16th and 18th are playing slightly downwind, left to right, so they're pretty easy birdie holes," said Watson.
"I wasn't worried about Senden. I was just trying to get back to even-par."
Watson took advantage of both the 16th and 18th holes and also made inroads on par at the second, fifth and seventh.
"It's fun to finish the way I did and get ready to go to the next tournament. You feel lighter, you don't feel heavy," said the captain of the United States team that will take on holders Europe at the Ryder Cup in Scotland in September.
"You don't feel like you have a burden that you're taking with you. Keep the engine running if you can, wake up every morning not in too much pain and go from there."
Watson said he felt he could have posted an even better round than 68.
"It was a very good day from tee to green but it wasn't a particularly good day of putting," he added.
"I had a lot of 15, 20, 25-footers where I really didn't make a very good attempt. It never looked like they were going to go in."
Watson said he would leave for his next assignment at the Royal Porthcawl Golf Club in Wales with an extra spring in his step.
"It gives me encouragement for the Senior British Open," he added of the July 24-27 event. "I don't know anything about the golf course but it's fun to finish here the way I did and get ready to go to the next tournament."
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