Reigning Masters champion Scott, who in April became the first Aussie to win a green jacket, birdied three of his first seven holes in the second round and made the turn at seven under par for the tournament, two under for the day.
Day, Westwood and Germany’s Martin Kaymer were on four-under and the only players on the course within five strokes of Scott with half the field set for an afternoon start.
Westwood and Day, who have both endured several painful near-misses at majors, made early birdies to match Scott's lead as he began by teeing off at the 10th hole in heavy showers.
But as his rivals faltered in the downpour that drenched the 7,163-yard layout, Scott responded with a chip-in birdie at the 10th and dropped a tricky double-breaking 10-foot birdie putt into the left side of the cup at the par-5 13th to reach seven-under.
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