The 35-year-old American left-hander, who beat Louis Oosthuizen in a playoff for the 2012 crown, fired a four-under par 68 to stand on seven-under 137 after 36 holes, grabbing a three-shot lead over Australian John Senden in quest for his second career major title.
"I felt really good," Watson said. "It's not science here. It's try to hit the greens and if you're hitting the greens that means you're obviously hitting your tee shots well. That's what I've done the last two days and it's worked out so far."
"You're so focused on what you are doing, you are not really thinking you have just had three in a row, four in a row," Watson said.
"It's one of those things. Everyone has had that stretch before, playing with their buddies or playing in a tournament, so it's not that big a deal when we think about it.
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"But at the Masters, it makes it a big deal."
Watson, whose first win after claiming the green jacket came only two months ago at Riviera, struggled with demands on him last year as defending champion and only managed a share of 50th.