In Road to the Masters mode, this is the second tournament in which you'll compete, following your 9-hole "tryout". It should be pretty simple to win this one, as your competition will all finish well above par (second place in my game finished +6). Follow your caddie's advice if you're new to the series and you really can't go wrong. Don't forget that clicking the left stick will let you practice your swing if you're looking to make a shot that's a low percentage swing.
Once you finish first in the 18-hole tournament the Achievement will unlock. Note that you can jump straight to the tournament if you wish - you don't need to first win the practice or sponsor challenges.